//$ nobt
//$ nocpp

/**
 * @file avir.h
 *
 * @brief The "main" inclusion file with all required classes and functions.
 *
 * This is the "main" inclusion file for the "AVIR" image resizer. This
 * inclusion file contains implementation of the AVIR image resizing algorithm
 * in its entirety. Also includes several classes and functions that can be
 * useful elsewhere.
 *
 * AVIR Copyright (c) 2015-2019 Aleksey Vaneev
 *
 * @mainpage
 *
 * @section intro_sec Introduction
 *
 * Description is available at https://github.com/avaneev/avir
 *
 * AVIR is devoted to women. Your digital photos can look good at any size!
 *
 * @section license License
 *
 * AVIR License Agreement
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2015-2019 Aleksey Vaneev
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 * Please credit the author of this library in your documentation in the
 * following way: "AVIR image resizing algorithm designed by Aleksey Vaneev"
 *
 * @version 2.4
 */

#ifndef AVIR_CIMAGERESIZER_INCLUDED
#define AVIR_CIMAGERESIZER_INCLUDED

#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

namespace avir {

/**
 * The macro defines AVIR version string.
 */

#define AVIR_VERSION "2.4"

/**
 * The macro equals to "pi" constant, fills 53-bit floating point mantissa.
 * Undefined at the end of file.
 */

#define AVIR_PI 3.1415926535897932

/**
 * The macro equals to "pi divided by 2" constant, fills 53-bit floating
 * point mantissa. Undefined at the end of file.
 */

#define AVIR_PId2 1.5707963267948966

/**
 * Rounding function, based on the (int) typecast. Biased result. Not suitable
 * for numbers >= 2^31.
 *
 * @param d Value to round.
 * @return Rounded value. Some bias may be introduced.
 */

template< class T >
inline T round( const T d )
{
    return( d < 0.0 ? -(T) (int) ( (T) 0.5 - d ) : (T) (int) ( d + (T) 0.5 ));
}

/**
 * Template function "clamps" (clips) the specified value so that it is not
 * lesser than "minv", and not greater than "maxv".
 *
 * @param Value Value to clamp.
 * @param minv Minimal allowed value.
 * @param maxv Maximal allowed value.
 * @return The clamped value.
 */

template< class T >
inline T clamp( const T& Value, const T minv, const T maxv )
{
    if( Value < minv )
    {
        return( minv );
    }
    else
    if( Value > maxv )
    {
        return( maxv );
    }
    else
    {
        return( Value );
    }
}

/**
 * Power 2.4 approximation function, designed for sRGB gamma correction.
 *
 * @param x Argument, in the range 0.09 to 1.
 * @return Value raised into power 2.4, approximate.
 */

template< class T >
inline T pow24_sRGB( const T x )
{
    const double x2 = x * x;
    const double x3 = x2 * x;
    const double x4 = x2 * x2;

    return( (T) ( 0.0985766365536824 + 0.839474952656502 * x2 +
        0.363287814061725 * x3 - 0.0125559718896615 /
        ( 0.12758338921578 + 0.290283465468235 * x ) -
        0.231757513261358 * x - 0.0395365717969074 * x4 ));
}

/**
 * Power 1/2.4 approximation function, designed for sRGB gamma correction.
 *
 * @param x Argument, in the range 0.003 to 1.
 * @return Value raised into power 1/2.4, approximate.
 */

template< class T >
inline T pow24i_sRGB( const T x )
{
    const double sx = sqrt( x );
    const double ssx = sqrt( sx );
    const double sssx = sqrt( ssx );

    return( (T) ( 0.000213364515060263 + 0.0149409239419218 * x +
        0.433973412731747 * sx + ssx * ( 0.659628181609715 * sssx -
        0.0380957908841466 - 0.0706476137208521 * sx )));
}

/**
 * Function approximately linearizes the sRGB gamma value.
 *
 * @param s sRGB gamma value, in the range 0 to 1.
 * @return Linearized sRGB gamma value, approximated.
 */

template< class T >
inline T convertSRGB2Lin( const T s )
{
    const T a = (T) 0.055;

    if( s <= (T) 0.04045 )
    {
        return( s / (T) 12.92 );
    }

    return( pow24_sRGB(( s + a ) / ( (T) 1 + a )));
}

/**
 * Function approximately de-linearizes the linear gamma value.
 *
 * @param s Linear gamma value, in the range 0 to 1.
 * @return sRGB gamma value, approximated.
 */

template< class T >
inline T convertLin2SRGB( const T s )
{
    const T a = (T) 0.055;

    if( s <= (T) 0.0031308 )
    {
        return( (T) 12.92 * s );
    }

    return(( (T) 1 + a ) * pow24i_sRGB( s ) - a );
}

/**
 * Function converts (via typecast) specified array of type T1 values of
 * length l into array of type T2 values. If T1 is the same as T2, copy
 * operation is performed. When copying data at overlapping address spaces,
 * "op" should be lower than "ip".
 *
 * @param ip Input buffer.
 * @param[out] op Output buffer.
 * @param l The number of elements to copy.
 * @param ip Input buffer pointer increment.
 * @param op Output buffer pointer increment.
 */

template< class T1, class T2 >
inline void copyArray( const T1* ip, T2* op, int l,
    const int ipinc = 1, const int opinc = 1 )
{
    while( l > 0 )
    {
        *op = (T2) *ip;
        op += opinc;
        ip += ipinc;
        l--;
    }
}

/**
 * Function adds values located in array "ip" to array "op".
 *
 * @param ip Input buffer.
 * @param[out] op Output buffer.
 * @param l The number of elements to add.
 * @param ip Input buffer pointer increment.
 * @param op Output buffer pointer increment.
 */

template< class T1, class T2 >
inline void addArray( const T1* ip, T2* op, int l,
    const int ipinc = 1, const int opinc = 1 )
{
    while( l > 0 )
    {
        *op += *ip;
        op += opinc;
        ip += ipinc;
        l--;
    }
}

/**
 * Function that replicates a set of adjacent elements several times in a row.
 * This operation is usually used to replicate pixels at the start or end of
 * image's scanline.
 *
 * @param ip Source array.
 * @param ipl Source array length (usually 1..4, but can be any number).
 * @param[out] op Destination buffer.
 * @param l Number of times the source array should be replicated (the
 * destination buffer should be able to hold ipl * l number of elements).
 * @param opinc Destination buffer position increment after replicating the
 * source array. This value should be equal to at least ipl.
 */

template< class T1, class T2 >
inline void replicateArray( const T1* const ip, const int ipl, T2* op, int l,
    const int opinc )
{
    if( ipl == 1 )
    {
        while( l > 0 )
        {
            op[ 0 ] = ip[ 0 ];
            op += opinc;
            l--;
        }
    }
    else
    if( ipl == 4 )
    {
        while( l > 0 )
        {
            op[ 0 ] = ip[ 0 ];
            op[ 1 ] = ip[ 1 ];
            op[ 2 ] = ip[ 2 ];
            op[ 3 ] = ip[ 3 ];
            op += opinc;
            l--;
        }
    }
    else
    if( ipl == 3 )
    {
        while( l > 0 )
        {
            op[ 0 ] = ip[ 0 ];
            op[ 1 ] = ip[ 1 ];
            op[ 2 ] = ip[ 2 ];
            op += opinc;
            l--;
        }
    }
    else
    if( ipl == 2 )
    {
        while( l > 0 )
        {
            op[ 0 ] = ip[ 0 ];
            op[ 1 ] = ip[ 1 ];
            op += opinc;
            l--;
        }
    }
    else
    {
        while( l > 0 )
        {
            int i;

            for( i = 0; i < ipl; i++ )
            {
                op[ i ] = ip[ i ];
            }

            op += opinc;
            l--;
        }
    }
}

/**
 * Function calculates frequency response of the specified FIR filter at the
 * specified circular frequency. Phase can be calculated as atan2( im, re ).
 * Function uses computationally-efficient oscillators instead of "cos" and
 * "sin" functions.
 *
 * @param flt FIR filter's coefficients.
 * @param fltlen Number of coefficients (taps) in the filter.
 * @param th Circular frequency [0; pi].
 * @param[out] re0 Resulting real part of the complex frequency response.
 * @param[out] im0 Resulting imaginary part of the complex frequency response.
 * @param fltlat Filter's latency in samples (taps).
 */

template< class T >
inline void calcFIRFilterResponse( const T* flt, int fltlen,
    const double th, double& re0, double& im0, const int fltlat = 0 )
{
    const double sincr = 2.0 * cos( th );
    double cvalue1;
    double svalue1;

    if( fltlat == 0 )
    {
        cvalue1 = 1.0;
        svalue1 = 0.0;
    }
    else
    {
        cvalue1 = cos( -fltlat * th );
        svalue1 = sin( -fltlat * th );
    }

    double cvalue2 = cos( -( fltlat + 1 ) * th );
    double svalue2 = sin( -( fltlat + 1 ) * th );

    double re = 0.0;
    double im = 0.0;

    while( fltlen > 0 )
    {
        re += cvalue1 * flt[ 0 ];
        im += svalue1 * flt[ 0 ];
        flt++;
        fltlen--;

        double tmp = cvalue1;
        cvalue1 = sincr * cvalue1 - cvalue2;
        cvalue2 = tmp;

        tmp = svalue1;
        svalue1 = sincr * svalue1 - svalue2;
        svalue2 = tmp;
    }

    re0 = re;
    im0 = im;
}

/**
 * Function normalizes FIR filter so that its frequency response at DC is
 * equal to DCGain.
 *
 * @param[in,out] p Filter coefficients.
 * @param l Filter length.
 * @param DCGain Filter's gain at DC.
 * @param pstep "p" array step.
 */

template< class T >
inline void normalizeFIRFilter( T* const p, const int l, const double DCGain,
    const int pstep = 1 )
{
    double s = 0.0;
    T* pp = p;
    int i = l;

    while( i > 0 )
    {
        s += *pp;
        pp += pstep;
        i--;
    }

    s = DCGain / s;
    pp = p;
    i = l;

    while( i > 0 )
    {
        *pp = (T) ( *pp * s );
        pp += pstep;
        i--;
    }
}

/**
 * @brief Memory buffer class for element array storage, with capacity
 * tracking.
 *
 * Allows easier handling of memory blocks allocation and automatic
 * deallocation for arrays (buffers) consisting of elements of specified
 * class. Tracks buffer's capacity in "int" variable; unsuitable for
 * allocation of very large memory blocks (with more than 2 billion elements).
 *
 * This class manages memory space only - it does not perform element class
 * construction (initialization) operations. Buffer's required memory address
 * alignment specification is supported.
 *
 * Uses standard library to allocate and deallocate memory.
 *
 * @tparam T Buffer element's type.
 * @tparam capint Buffer capacity's type to use. Use size_t for large buffers.
 */

template< class T, typename capint = int >
class CBuffer
{
public:
    CBuffer()
        : Data( nullptr )
        , DataAligned( nullptr )
        , Capacity( 0 )
        , Alignment( 0 )
    {
    }

    /**
     * Constructor creates the buffer with the specified capacity.
     *
     * @param aCapacity Buffer's capacity.
     * @param aAlignment Buffer's required memory address alignment. 0 - use
     * stdlib's default alignment.
     */

    CBuffer( const capint aCapacity, const int aAlignment = 0 )
    {
        allocinit( aCapacity, aAlignment );
    }

    CBuffer( const CBuffer& Source )
    {
        allocinit( Source.Capacity, Source.Alignment );
        memcpy( DataAligned, Source.DataAligned, Capacity * sizeof( T ));
    }

    ~CBuffer()
    {
        freeData();
    }

    CBuffer& operator = ( const CBuffer& Source )
    {
        alloc( Source.Capacity, Source.Alignment );
        memcpy( DataAligned, Source.DataAligned, Capacity * sizeof( T ));
        return( *this );
    }

    /**
     * Function allocates memory so that the specified number of elements
     * can be stored in *this buffer object.
     *
     * @param aCapacity Storage for this number of elements to allocate.
     * @param aAlignment Buffer's required memory address alignment,
     * power-of-2 values only. 0 - use stdlib's default alignment.
     */

    void alloc( const capint aCapacity, const int aAlignment = 0 )
    {
        freeData();
        allocinit( aCapacity, aAlignment );
    }

    /**
     * Function deallocates any previously allocated buffer.
     */

    void free()
    {
        freeData();
        Data = nullptr;
        DataAligned = nullptr;
        Capacity = 0;
        Alignment = 0;
    }

    /**
     * @return The capacity of the element buffer.
     */

    capint getCapacity() const
    {
        return( Capacity );
    }

    /**
     * Function "forces" *this buffer to have an arbitary capacity. Calling
     * this function invalidates all further operations except deleting *this
     * object. This function should not be usually used at all. Function can
     * be used to "model" certain buffer capacity without calling a costly
     * memory allocation function.
     *
     * @param NewCapacity A new "forced" capacity.
     */

    void forceCapacity( const capint NewCapacity )
    {
        Capacity = NewCapacity;
    }

    /**
     * Function reallocates *this buffer to a larger size so that it will be
     * able to hold the specified number of elements. Downsizing is not
     * performed. Alignment is not changed.
     *
     * @param NewCapacity New (increased) capacity.
     * @param DoDataCopy "True" if data in the buffer should be retained.
     */

    void increaseCapacity( const capint NewCapacity,
        const bool DoDataCopy = true )
    {
        if( NewCapacity < Capacity )
        {
            return;
        }

        if( DoDataCopy )
        {
            const capint PrevCapacity = Capacity;
            T* const PrevData = Data;
            T* const PrevDataAligned = DataAligned;

            allocinit( NewCapacity, Alignment );
            memcpy( DataAligned, PrevDataAligned, PrevCapacity * sizeof( T ));

            :: free( PrevData );
        }
        else
        {
            :: free( Data );
            allocinit( NewCapacity, Alignment );
        }
    }

    /**
     * Function "truncates" (reduces) capacity of the buffer without
     * reallocating it. Alignment is not changed.
     *
     * @param NewCapacity New required capacity.
     */

    void truncateCapacity( const capint NewCapacity )
    {
        if( NewCapacity >= Capacity )
        {
            return;
        }

        Capacity = NewCapacity;
    }

    /**
     * Function increases capacity so that the specified number of
     * elements can be stored. This function increases the previous capacity
     * value by third the current capacity value until space for the required
     * number of elements is available. Alignment is not changed.
     *
     * @param ReqCapacity Required capacity.
     */

    void updateCapacity( const capint ReqCapacity )
    {
        if( ReqCapacity <= Capacity )
        {
            return;
        }

        capint NewCapacity = Capacity;

        while( NewCapacity < ReqCapacity )
        {
            NewCapacity += NewCapacity / 3 + 1;
        }

        increaseCapacity( NewCapacity );
    }

    operator T* () const
    {
        return( DataAligned );
    }

private:
    T* Data; ///< Element buffer pointer.
        ///<
    T* DataAligned; ///< Memory address-aligned element buffer pointer.
        ///<
    capint Capacity; ///< Element buffer capacity.
        ///<
    int Alignment; ///< Memory address alignment in use. 0 - use stdlib's
        ///< default alignment.
        ///<

    /**
     * Internal element buffer allocation function used during object
     * construction.
     *
     * @param aCapacity Storage for this number of elements to allocate.
     * @param aAlignment Buffer's required memory address alignment. 0 - use
     * stdlib's default alignment.
     */

    void allocinit( const capint aCapacity, const int aAlignment )
    {
        if( aAlignment == 0 )
        {
            Data = (T*) :: malloc( aCapacity * sizeof( T ));
            DataAligned = Data;
            Alignment = 0;
        }
        else
        {
            Data = (T*) :: malloc( aCapacity * sizeof( T ) + aAlignment );
            DataAligned = alignptr( Data, aAlignment );
            Alignment = aAlignment;
        }

        Capacity = aCapacity;
    }

    /**
     * Function frees a previously allocated Data buffer.
     */

    void freeData()
    {
        :: free( Data );
    }

    /**
     * Function modifies the specified pointer so that it becomes memory
     * address-aligned.
     *
     * @param ptr Pointer to align.
     * @param align Alignment in bytes to apply.
     * @return Pointer aligned to align bytes. Works with power-of-2
     * alignments only. If no alignment is necessary, "align" bytes will be
     * added to the pointer value.
     */

    template< class Tp >
    inline Tp alignptr( const Tp ptr, const uintptr_t align )
    {
        return( (Tp) ( (uintptr_t) ptr + align -
            ( (uintptr_t) ptr & ( align - 1 ))) );
    }
};

/**
 * Function optimizes the length of the symmetric-odd FIR filter by removing
 * left- and rightmost elements that are below specific threshold.
 *
 * Synthetic test shows that filter gets optimized in 2..3% of cases and in
 * each such case optimization reduces filter length by 6..8%. Optimization,
 * however, may skew the results of algorithm modeling and complexity
 * calculation leading to a choice of a less optimal algorithm.
 *
 * @param[in,out] Flt Buffer that contains filter being optimized.
 * @param[in,out] FltLatency Variable that holds the current latency of the
 * filter. May be adjusted on function return.
 * @param Threshold Threshold level.
 */

template< class T >
inline void optimizeFIRFilter( CBuffer< T >& Flt, int& FltLatency,
    T const Threshold = (T) 0.00001 )
{
    int i;

    // Optimize length.

    for( i = 0; i <= FltLatency; i++ )
    {
        if( fabs( Flt[ i ]) >= Threshold || i == FltLatency )
        {
            if( i > 0 )
            {
                const int NewCapacity = Flt.getCapacity() - i * 2;
                copyArray( &Flt[ i ], &Flt[ 0 ], NewCapacity );
                Flt.truncateCapacity( NewCapacity );
                FltLatency -= i;
            }

            break;
        }
    }
}

/**
 * @brief Array of structured objects.
 *
 * Implements allocation of a linear array of objects of class T (which are
 * initialized), addressable via operator[]. Each object is created via the
 * "operator new". New object insertions are quick since implementation uses
 * prior space allocation (capacity), thus not requiring frequent memory block
 * reallocations.
 *
 * @tparam T Array element's type.
 */

template< class T >
class CStructArray
{
public:
    CStructArray()
        : ItemCount( 0 )
    {
    }

    CStructArray( const CStructArray& Source )
        : ItemCount( 0 )
        , Items( Source.getItemCount() )
    {
        while( ItemCount < Source.getItemCount() )
        {
            Items[ ItemCount ] = new T( Source[ ItemCount ]);
            ItemCount++;
        }
    }

    ~CStructArray()
    {
        clear();
    }

    CStructArray& operator = ( const CStructArray& Source )
    {
        clear();

        const int NewCount = Source.ItemCount;
        Items.updateCapacity( NewCount );

        while( ItemCount < NewCount )
        {
            Items[ ItemCount ] = new T( Source[ ItemCount ]);
            ItemCount++;
        }

        return( *this );
    }

    T& operator []( const int Index )
    {
        return( *Items[ Index ]);
    }

    const T& operator []( const int Index ) const
    {
        return( *Items[ Index ]);
    }

    /**
     * Function creates a new object of type T with the default constructor
     * and adds this object to the array.
     *
     * @return Reference to a newly added object.
     */

    T& add()
    {
        if( ItemCount == Items.getCapacity() )
        {
            Items.increaseCapacity( ItemCount * 3 / 2 + 1 );
        }

        Items[ ItemCount ] = new T();
        ItemCount++;

        return( (*this)[ ItemCount - 1 ]);
    }

    /**
     * Function changes number of allocated items. New items are created with
     * the default constructor. If NewCount is below the current item count,
     * items that are above NewCount range will be destructed.
     *
     * @param NewCount New requested item count.
     */

    void setItemCount( const int NewCount )
    {
        if( NewCount > ItemCount )
        {
            Items.increaseCapacity( NewCount );

            while( ItemCount < NewCount )
            {
                Items[ ItemCount ] = new T();
                ItemCount++;
            }
        }
        else
        {
            while( ItemCount > NewCount )
            {
                ItemCount--;
                delete Items[ ItemCount ];
            }
        }
    }

    /**
     * Function erases all items of *this array.
     */

    void clear()
    {
        while( ItemCount > 0 )
        {
            ItemCount--;
            delete Items[ ItemCount ];
        }
    }

    /**
     * @return The number of allocated items.
     */

    int getItemCount() const
    {
        return( ItemCount );
    }

private:
    int ItemCount; ///< The number of items available in the array.
        ///<
    CBuffer< T* > Items; ///< Element buffer.
        ///<
};

/**
 * @brief Sine signal generator class.
 *
 * Class implements sine signal generator without biasing, with
 * constructor-based initalization only. This generator uses oscillator
 * instead of "sin" function.
 */

class CSineGen
{
public:
    /**
     * Constructor initializes *this sine signal generator.
     *
     * @param si Sine function increment, in radians.
     * @param ph Starting phase, in radians. Add 0.5 * AVIR_PI for cosine
     * function.
     */

    CSineGen( const double si, const double ph )
        : svalue1( sin( ph ))
        , svalue2( sin( ph - si ))
        , sincr( 2.0 * cos( si ))
    {
    }

    /**
     * @return The next value of the sine function, without biasing.
     */

    double generate()
    {
        const double res = svalue1;

        svalue1 = sincr * res - svalue2;
        svalue2 = res;

        return( res );
    }

private:
    double svalue1; ///< Current sine value.
        ///<
    double svalue2; ///< Previous sine value.
        ///<
    double sincr; ///< Sine value increment.
        ///<
};

/**
 * @brief Peaked Cosine window function generator class.
 *
 * Class implements Peaked Cosine window function generator. Generates the
 * right-handed half of the window function. The Alpha parameter of this
 * window function offers the control of the balance between the early and
 * later taps of the filter. E.g. at Alpha=1 both early and later taps are
 * attenuated, but at Alpha=4 mostly later taps are attenuated. This offers a
 * great control over ringing artifacts produced by a low-pass filter in image
 * processing, without compromising achieved image sharpness.
 */

class CDSPWindowGenPeakedCosine
{
public:
    /**
     * Constructor initializes *this window function generator.
     *
     * @param aAlpha Alpha parameter, affects the peak shape (peak
     * augmentation) of the window function. Should be >= 1.0.
     * @param aLen2 Half filter's length (non-truncated).
     */

    CDSPWindowGenPeakedCosine( const double aAlpha, const double aLen2 )
        : Alpha( aAlpha )
        , Len2( aLen2 )
        , wn( 0 )
        , w1( AVIR_PId2 / Len2, AVIR_PI * 0.5 )
    {
    }

    /**
     * @return The next Peaked Cosine window function coefficient.
     */

    double generate()
    {
        const double h = pow( wn / Len2, Alpha );
        wn++;

        return( w1.generate() * ( 1.0 - h ));
    }

private:
    double Alpha; ///< Alpha parameter, affects the peak shape of window.
        ///<
    double Len2; ///< Half length of the window function.
        ///<
    int wn; ///< Window function integer position. 0 - center of the
        ///< window function.
        ///<
    CSineGen w1; ///< Sine-wave generator.
        ///<
};

/**
 * @brief FIR filter-based equalizer generator.
 *
 * Class implements an object used to generate symmetric-odd FIR filters with
 * the specified frequency response (aka paragraphic equalizer). The
 * calculated filter is windowed by the Peaked Cosine window function.
 *
 * In image processing, due to short length of filters being used (6-8 taps)
 * the resulting frequency response of the filter is approximate and may be
 * mathematically imperfect, but still adequate to the visual requirements.
 *
 * On a side note, this equalizer generator can be successfully used for audio
 * signal equalization as well: for example, it is used in almost the same
 * form in Voxengo Marvel GEQ equalizer plug-in.
 *
 * Filter generation is based on decomposition of frequency range into
 * spectral bands, with each band represented by linear and ramp "kernels".
 * When the filter is built, these kernels are combined together with
 * different weights that approximate the required frequency response.
 */

class CDSPFIREQ
{
public:
    /**
     * Function initializes *this object with the required parameters. The
     * gain of frequencies beyond the MinFreq..MaxFreq range are controlled by
     * the first and the last band's gain.
     *
     * @param SampleRate Processing sample rate (use 2 for image processing).
     * @param aFilterLength Required filter length in samples (taps). The
     * actual filter length is truncated to an integer value.
     * @param aBandCount Number of band crossover points required to control,
     * including bands at MinFreq and MaxFreq.
     * @param MinFreq Minimal frequency that should be controlled.
     * @param MaxFreq Maximal frequency that should be controlled.
     * @param IsLogBands "True" if the bands should be spaced logarithmically.
     * @param WFAlpha Peaked Cosine window function's Alpha parameter.
     */

    void init( const double SampleRate, const double aFilterLength,
        const int aBandCount, const double MinFreq, const double MaxFreq,
        const bool IsLogBands, const double WFAlpha )
    {
        FilterLength = aFilterLength;
        BandCount = aBandCount;

        CenterFreqs.alloc( BandCount );

        z = (int) ceil( FilterLength * 0.5 );
        zi = z + ( z & 1 );
        z2 = z * 2;

        CBuffer< double > oscbuf( z2 );
        initOscBuf( oscbuf );

        CBuffer< double > winbuf( z );
        initWinBuf( winbuf, WFAlpha );

        UseFirstVirtBand = ( MinFreq > 0.0 );
        const int k = zi * ( BandCount + ( UseFirstVirtBand ? 1 : 0 ));
        Kernels1.alloc( k );
        Kernels2.alloc( k );

        double m; // Frequency step multiplier.
        double mo; // Frequency step offset (addition).

        if( IsLogBands )
        {
            m = exp( log( MaxFreq / MinFreq ) / ( BandCount - 1 ));
            mo = 0.0;
        }
        else
        {
            m = 1.0;
            mo = ( MaxFreq - MinFreq ) / ( BandCount - 1 );
        }

        double f = MinFreq;
        double x1 = 0.0;
        double x2;
        int si;

        if( UseFirstVirtBand )
        {
            si = 0;
        }
        else
        {
            si = 1;
            CenterFreqs[ 0 ] = 0.0;
            f = f * m + mo;
        }

        double* kernbuf1 = &Kernels1[ 0 ];
        double* kernbuf2 = &Kernels2[ 0 ];
        int i;

        for( i = si; i < BandCount; i++ )
        {
            x2 = f * 2.0 / SampleRate;
            CenterFreqs[ i ] = x2;

            fillBandKernel( x1, x2, kernbuf1, kernbuf2, oscbuf, winbuf );

            kernbuf1 += zi;
            kernbuf2 += zi;
            x1 = x2;
            f = f * m + mo;
        }

        if( x1 < 1.0 )
        {
            UseLastVirtBand = true;
            fillBandKernel( x1, 1.0, kernbuf1, kernbuf2, oscbuf, winbuf );
        }
        else
        {
            UseLastVirtBand = false;
        }
    }

    /**
     * @return Filter's length, in samples (taps).
     */

    int getFilterLength() const
    {
        return( z2 - 1 );
    }

    /**
     * @return Filter's latency (group delay), in samples (taps).
     */

    int getFilterLatency() const
    {
        return( z - 1 );
    }

    /**
     * Function creates symmetric-odd FIR filter with the specified gain
     * levels at band crossover points.
     *
     * @param BandGains Array of linear gain levels, count=BandCount specified
     * in the init() function.
     * @param[out] Filter Output filter buffer, length = getFilterLength().
     */

    void buildFilter( const double* const BandGains, double* const Filter )
    {
        const double* kernbuf1 = &Kernels1[ 0 ];
        const double* kernbuf2 = &Kernels2[ 0 ];
        double x1 = 0.0;
        double y1 = BandGains[ 0 ];
        double x2;
        double y2;

        int i;
        int si;

        if( UseFirstVirtBand )
        {
            si = 1;
            x2 = CenterFreqs[ 0 ];
            y2 = y1;
        }
        else
        {
            si = 2;
            x2 = CenterFreqs[ 1 ];
            y2 = BandGains[ 1 ];
        }

        copyBandKernel( Filter, kernbuf1, kernbuf2, y1 - y2,
            x1 * y2 - x2 * y1 );

        kernbuf1 += zi;
        kernbuf2 += zi;
        x1 = x2;
        y1 = y2;

        for( i = si; i < BandCount; i++ )
        {
            x2 = CenterFreqs[ i ];
            y2 = BandGains[ i ];

            addBandKernel( Filter, kernbuf1, kernbuf2, y1 - y2,
                x1 * y2 - x2 * y1 );

            kernbuf1 += zi;
            kernbuf2 += zi;
            x1 = x2;
            y1 = y2;
        }

        if( UseLastVirtBand )
        {
            addBandKernel( Filter, kernbuf1, kernbuf2, y1 - y2,
                x1 * y2 - y1 );
        }

        for( i = 0; i < z - 1; i++ )
        {
            Filter[ z + i ] = Filter[ z - 2 - i ];
        }
    }

    /**
     * Function calculates filter's length (in samples) and latency depending
     * on the required non-truncated filter length.
     *
     * @param aFilterLength Required filter length in samples (non-truncated).
     * @param[out] Latency Resulting latency (group delay) of the filter,
     * in samples (taps).
     * @return Filter length in samples (taps).
     */

    static int calcFilterLength( const double aFilterLength, int& Latency )
    {
        const int l = (int) ceil( aFilterLength * 0.5 );
        Latency = l - 1;

        return( l * 2 - 1 );
    }

private:
    double FilterLength; ///< Length of filter.
        ///<
    int z; ///< Equals (int) ceil( FilterLength * 0.5 ).
        ///<
    int zi; ///< Equals "z" if z is even, or z + 1 if z is odd. Used as a
        ///< Kernels1 and Kernels2 size multiplier and kernel buffer increment
        ///< to make sure each kernel buffer is 16-byte aligned.
        ///<
    int z2; ///< Equals z * 2.
        ///<
    int BandCount; ///< Number of controllable bands.
        ///<
    CBuffer< double > CenterFreqs; ///< Center frequencies for all bands,
        ///< normalized to 0.0-1.0 range.
        ///<
    CBuffer< double > Kernels1; ///< Half-length kernel buffers for each
        ///< spectral band (linear part).
        ///<
    CBuffer< double > Kernels2; ///< Half-length kernel buffers for each
        ///< spectral band (ramp part).
        ///<
    bool UseFirstVirtBand; ///< "True" if the first virtual band
        ///< (between 0.0 and MinFreq) should be used. The first virtual band
        ///< won't be used if MinFreq equals 0.0.
        ///<
    bool UseLastVirtBand; ///< "True" if the last virtual band (between
        ///< MaxFreq and SampleRate * 0.5) should be used. The last virtual
        ///< band won't be used if MaxFreq * 2.0 equals SampleRate.
        ///<

    /**
     * Function initializes the "oscbuf" used in the fillBandKernel()
     * function.
     *
     * @param oscbuf Oscillator buffer, length = z * 2.
     */

    void initOscBuf( double* oscbuf ) const
    {
        int i = z;

        while( i > 0 )
        {
            oscbuf[ 0 ] = 0.0;
            oscbuf[ 1 ] = 1.0;
            oscbuf += 2;
            i--;
        }
    }

    /**
     * Function initializes window function buffer. This function generates
     * Peaked Cosine window function.
     *
     * @param winbuf Windowing buffer.
     * @param Alpha Peaked Cosine alpha parameter.
     */

    void initWinBuf( double* winbuf, const double Alpha ) const
    {
        CDSPWindowGenPeakedCosine wf( Alpha, FilterLength * 0.5 );
        int i;

        for( i = 1; i <= z; i++ )
        {
            winbuf[ z - i ] = wf.generate();
        }
    }

    /**
     * Function fills first half of symmetric-odd FIR kernel for the band.
     * This function should be called successively for adjacent bands.
     * Previous band's x2 should be equal to current band's x1. A band kernel
     * consists of 2 elements: linear kernel and ramp kernel.
     *
     * @param x1 Band's left corner frequency (0..1).
     * @param x2 Band's right corner frequency (0..1).
     * @param kernbuf1 Band kernel buffer 1 (linear part), length = z.
     * @param kernbuf2 Band kernel buffer 2 (ramp part), length = z.
     * @param oscbuf Oscillation buffer. Before the first call of the
     * fillBandKernel() should be initialized with the call of the
     * initOscBuf() function.
     * @param winbuf Buffer that contains windowing function.
     */

    void fillBandKernel( const double x1, const double x2, double* kernbuf1,
        double* kernbuf2, double* oscbuf, const double* const winbuf )
    {
        const double s2_incr = AVIR_PI * x2;
        const double s2_coeff = 2.0 * cos( s2_incr );

        double s2_value1 = sin( s2_incr * ( -z + 1 ));
        double c2_value1 = sin( s2_incr * ( -z + 1 ) + AVIR_PI * 0.5 );
        oscbuf[ 0 ] = sin( s2_incr * -z );
        oscbuf[ 1 ] = sin( s2_incr * -z + AVIR_PI * 0.5 );

        int ks;

        for( ks = 1; ks < z; ks++ )
        {
            const int ks2 = ks * 2;
            const double s1_value1 = oscbuf[ ks2 ];
            const double c1_value1 = oscbuf[ ks2 + 1 ];
            oscbuf[ ks2 ] = s2_value1;
            oscbuf[ ks2 + 1 ] = c2_value1;

            const double x = AVIR_PI * ( ks - z );
            const double v0 = winbuf[ ks - 1 ] / (( x1 - x2 ) * x );

            kernbuf1[ ks - 1 ] = ( x2 * s2_value1 - x1 * s1_value1 +
                ( c2_value1 - c1_value1 ) / x ) * v0;

            kernbuf2[ ks - 1 ] = ( s2_value1 - s1_value1 ) * v0;

            s2_value1 = s2_coeff * s2_value1 - oscbuf[ ks2 - 2 ];
            c2_value1 = s2_coeff * c2_value1 - oscbuf[ ks2 - 1 ];
        }

        kernbuf1[ z - 1 ] = ( x2 * x2 - x1 * x1 ) / ( x1 - x2 ) * 0.5;
        kernbuf2[ z - 1 ] = -1.0;
    }

    /**
     * Function copies band kernel's elements to the output buffer.
     *
     * @param outbuf Output buffer.
     * @param kernbuf1 Kernel buffer 1 (linear part).
     * @param kernbuf2 Kernel buffer 2 (ramp part).
     * @param c Multiplier for linear kernel element.
     * @param d Multiplier for ramp kernel element.
     */

    void copyBandKernel( double* outbuf, const double* const kernbuf1,
        const double* const kernbuf2, const double c, const double d ) const
    {
        int ks;

        for( ks = 0; ks < z; ks++ )
        {
            outbuf[ ks ] = c * kernbuf1[ ks ] + d * kernbuf2[ ks ];
        }
    }

    /**
     * Function adds band kernel's elements to the output buffer.
     *
     * @param outbuf Output buffer.
     * @param kernbuf1 Kernel buffer 1 (linear part).
     * @param kernbuf2 Kernel buffer 2 (ramp part).
     * @param c Multiplier for linear kernel element.
     * @param d Multiplier for ramp kernel element.
     */

    void addBandKernel( double* outbuf, const double* const kernbuf1,
        const double* const kernbuf2, const double c, const double d ) const
    {
        int ks;

        for( ks = 0; ks < z; ks++ )
        {
            outbuf[ ks ] += c * kernbuf1[ ks ] + d * kernbuf2[ ks ];
        }
    }
};

/**
 * @brief Low-pass filter windowed by Peaked Cosine window function.
 *
 * This class implements calculation of linear-phase symmetric-odd FIR
 * low-pass filter windowed by the Peaked Cosine window function, for image
 * processing applications.
 */

class CDSPPeakedCosineLPF
{
public:
    int fl2; ///< Half filter's length, excluding the peak value. This value
        ///< can be also used as filter's latency in samples (taps).
        ///<
    int FilterLen; ///< Filter's length in samples (taps).
        ///<

    /**
     * Constructor initalizes *this object.
     *
     * @param aLen2 Half-length (non-truncated) of low-pass filter, in samples
     * (taps).
     * @param aFreq2 Low-pass filter's corner frequency [0; pi].
     * @param aAlpha Peaked Cosine window function Alpha parameter.
     */

    CDSPPeakedCosineLPF( const double aLen2, const double aFreq2,
        const double aAlpha )
        : fl2( (int) ceil( aLen2 ) - 1 )
        , FilterLen( fl2 + fl2 + 1 )
        , Len2( aLen2 )
        , Freq2( aFreq2 )
        , Alpha( aAlpha )
    {
    }

    /**
     * Function generates a linear-phase low-pass filter windowed by Peaked
     * Cosine window function.
     *
     * @param[out] op Output buffer, length = FilterLen (fl2 * 2 + 1).
     * @param DCGain Required gain at DC. The resulting filter will be
     * normalized to achieve this DC gain.
     */

    template< class T >
    void generateLPF( T* op, const double DCGain )
    {
        CDSPWindowGenPeakedCosine wf( Alpha, Len2 );
        CSineGen f2( Freq2, 0.0 );

        op += fl2;
        T* op2 = op;
        f2.generate();
        int t = 1;

        *op = (T) ( Freq2 * wf.generate() / AVIR_PI );
        double s = *op;

        while( t <= fl2 )
        {
            const double v = f2.generate() * wf.generate() / t / AVIR_PI;
            op++;
            op2--;
            *op = (T) v;
            *op2 = (T) v;
            s += *op + *op2;
            t++;
        }

        t = FilterLen;
        s = DCGain / s;

        while( t > 0 )
        {
            *op2 = (T) ( *op2 * s );
            op2++;
            t--;
        }
    }

private:
    double Len2; ///< Half-length (non-truncated) of low-pass filter, in
        ///< samples (taps).
        ///<
    double Freq2; ///< Low-pass filter's corner frequency.
        ///<
    double Alpha; ///< Peaked Cosine window function Alpha parameter.
        ///<
};

/**
 * @brief Buffer class for parametrized low-pass filter.
 *
 * This class extends the CBuffer< double > class by adding several variables
 * that define a symmetric-odd FIR low-pass filter windowed by Peaked Cosine
 * window function. This class can be used to compare filters without
 * comparing their buffer contents.
 */

class CFltBuffer : public CBuffer< double >
{
public:
    double Len2; ///< Half-length (non-truncated) of low-pass filters, in
        ///< samples (taps).
        ///<
    double Freq; ///< Low-pass filter's corner frequency.
        ///<
    double Alpha; ///< Peaked Cosine window function Alpha parameter.
        ///<
    double DCGain; ///< DC gain applied to the filter.
        ///<

    CFltBuffer()
        : CBuffer< double >()
        , Len2( 0.0 )
        , Freq( 0.0 )
        , Alpha( 0.0 )
        , DCGain( 0.0 )
    {
    }

    /**
     * @param b2 Filter buffer to compare *this object to.
     * @return Operator returns "true" if both filters have same parameters.
     */

    bool operator == ( const CFltBuffer& b2 ) const
    {
        return( Len2 == b2.Len2 && Freq == b2.Freq && Alpha == b2.Alpha &&
            DCGain == b2.DCGain );
    }
};

/**
 * @brief Sinc function-based fractional delay filter bank.
 *
 * Class implements storage and initialization of a bank of sinc
 * function-based fractional delay filters, expressed as 1st order polynomial
 * interpolation coefficients. The filters are produced from a single "long"
 * windowed low-pass filter. Also supports 0th-order ("nearest neighbor")
 * interpolation.
 *
 * This class also supports multiplication of each fractional delay filter by
 * an external filter (usually a low-pass filter).
 *
 * @tparam fptype Specifies storage type of the filter coefficients bank. The
 * filters are initially calculated using the "double" precision.
 */

template< class fptype >
class CDSPFracFilterBankLin
{
public:
    CDSPFracFilterBankLin()
        : Order( -1 )
    {
    }

    /**
     * Copy constructor copies a limited set of parameters of the source
     * filter bank. The actual filters are not copied. Such copying is used
     * during filtering steps "modeling" stage. A further init() function
     * call is required.
     *
     * @param s Source filter bank.
     */

    void copyInitParams( const CDSPFracFilterBankLin& s )
    {
        WFLen2 = s.WFLen2;
        WFFreq = s.WFFreq;
        WFAlpha = s.WFAlpha;
        FracCount = s.FracCount;
        Order = s.Order;
        Alignment = s.Alignment;
        SrcFilterLen = s.SrcFilterLen;
        FilterLen = s.FilterLen;
        FilterSize = s.FilterSize;
        IsSrcTableBuilt = false;
        ExtFilter = s.ExtFilter;
        TableFillFlags.alloc( s.TableFillFlags.getCapacity() );
        int i;

        // Copy table fill flags, but shifted so that further initialization
        // is still possible (such feature should not be used, though).

        for( i = 0; i < TableFillFlags.getCapacity(); i++ )
        {
            TableFillFlags[ i ] = (uint8_t) ( s.TableFillFlags[ i ] << 2 );
        }
    }

    /**
     * Operator compares *this filter bank and another filter bank and returns
     * "true" if their parameters are equal. Alignment is not taken into
     * account.
     *
     * @param s Filter bank to compare to.
     * @return "True" if compared banks have equal parameters.
     */

    bool operator == ( const CDSPFracFilterBankLin& s ) const
    {
        return( Order == s.Order && WFLen2 == s.WFLen2 &&
            WFFreq == s.WFFreq && WFAlpha == s.WFAlpha &&
            FracCount == s.FracCount && ExtFilter == s.ExtFilter );
    }

    /**
     * Function initializes (builds) the filter bank based on the supplied
     * parameters. If the supplied parameters are equal to previously defined
     * parameters, function does nothing (alignment is assumed to be never
     * changing between the init() function calls).
     *
     * @param ReqFracCount Required number of fractional delays in the filter
     * bank. The minimal value is 2.
     * @param ReqOrder Required order of the interpolation polynomial
     * (0 or 1).
     * @param BaseLen Low-pass filter's base length, in samples (taps).
     * Affects the actual length of the filter and its overall steepness.
     * @param Cutoff Low-pass filter's normalized cutoff frequency [0; 1].
     * @param aWFAlpha Peaked Cosine window function's Alpha parameter.
     * @param aExtFilter External filter to apply to each fractional delay
     * filter.
     * @param aAlignment Memory alignment of the filter bank, power-of-2
     * value. 0 - use default stdlib alignment.
     * @param FltLenAlign Filter's length alignment, power-of-2 value.
     */

    void init( const int ReqFracCount, const int ReqOrder,
        const double BaseLen, const double Cutoff, const double aWFAlpha,
        const CFltBuffer& aExtFilter, const int aAlignment = 0,
        const int FltLenAlign = 1 )
    {
        double NewWFLen2 = 0.5 * BaseLen * ReqFracCount;
        double NewWFFreq = AVIR_PI * Cutoff / ReqFracCount;
        double NewWFAlpha = aWFAlpha;

        if( ReqOrder == Order && NewWFLen2 == WFLen2 && NewWFFreq == WFFreq &&
            NewWFAlpha == WFAlpha && ReqFracCount == FracCount &&
            aExtFilter == ExtFilter )
        {
            IsInitRequired = false;
            return;
        }

        WFLen2 = NewWFLen2;
        WFFreq = NewWFFreq;
        WFAlpha = NewWFAlpha;
        FracCount = ReqFracCount;
        Order = ReqOrder;
        Alignment = aAlignment;
        ExtFilter = aExtFilter;

        CDSPPeakedCosineLPF p( WFLen2, WFFreq, WFAlpha );
        SrcFilterLen = ( p.fl2 / ReqFracCount + 1 ) * 2;

        const int ElementSize = ReqOrder + 1;
        FilterLen = SrcFilterLen;

        if( ExtFilter.getCapacity() > 0 )
        {
            FilterLen += ExtFilter.getCapacity() - 1;
        }

        FilterLen = ( FilterLen + FltLenAlign - 1 ) & ~( FltLenAlign - 1 );
        FilterSize = FilterLen * ElementSize;
        IsSrcTableBuilt = false;
        IsInitRequired = true;
    }

    /**
     * @return The length of each fractional delay filter, in samples (taps).
     * Always an even value.
     */

    int getFilterLen() const
    {
        return( FilterLen );
    }

    /**
     * @return The number of fractional filters in use by *this bank.
     */

    int getFracCount() const
    {
        return( FracCount );
    }

    /**
     * @return The order of the interpolation polynomial.
     */

    int getOrder() const
    {
        return( Order );
    }

    /**
     * Function returns the pointer to the specified interpolation table
     * filter.
     *
     * @param i Filter (fractional delay) index, in the range 0 to
     * ReqFracCount - 1, inclusive.
     * @return Pointer to filter. Higher order polynomial coefficients are
     * stored after after previous order coefficients, separated by FilterLen
     * elements.
     */

    const fptype* getFilter( const int i )
    {
        if( !IsSrcTableBuilt )
        {
            buildSrcTable();
        }

        fptype* const Res = &Table[ i * FilterSize ];

        if(( TableFillFlags[ i ] & 2 ) == 0 )
        {
            createFilter( i );
            TableFillFlags[ i ] |= 2;

            if( Order > 0 )
            {
                createFilter( i + 1 );
                const fptype* const Res2 = Res + FilterSize;
                fptype* const op = Res + FilterLen;
                int j;

                // Create higher-order interpolation coefficients (linear
                // interpolation).

                for( j = 0; j < FilterLen; j++ )
                {
                    op[ j ] = Res2[ j ] - Res[ j ];
                }
            }
        }

        return( Res );
    }

    /**
     * Function makes sure all fractional delay filters were created.
     */

    void createAllFilters()
    {
        int i;

        for( i = 0; i < FracCount; i++ )
        {
            getFilter( i );
        }
    }

    /**
     * Function returns an approximate initialization complexity, expressed in
     * the number of multiply-add operations. This includes fractional delay
     * filters calculation and multiplication by an external filter. This
     * function can only be called after the init() function.
     *
     * @param FracUseMap Fractional delays use map, each element corresponds
     * to a single fractional delay, will be compared to the internal table
     * fill flags. This map should include 0 and 1 values only.
     * @return The complexity of the initialization, expressed in the number
     * of multiply-add operations.
     */

    int calcInitComplexity( const CBuffer< uint8_t >& FracUseMap ) const
    {
        const int FltInitCost = 65; // Cost to initialize a single sample
            // of the fractional delay filter.
        const int FltUseCost = FilterLen * Order +
            SrcFilterLen * ExtFilter.getCapacity(); // Cost to use a single
            // fractional delay filter.
        const int ucb[ 2 ] = { 0, FltUseCost };
        int ic;
        int i;

        if( IsInitRequired )
        {
            ic = FracCount * SrcFilterLen * FltInitCost;

            for( i = 0; i < FracCount; i++ )
            {
                ic += ucb[ FracUseMap[ i ]];
            }
        }
        else
        {
            ic = 0;

            for( i = 0; i < FracCount; i++ )
            {
                if( FracUseMap[ i ] != 0 )
                {
                    ic += ucb[ TableFillFlags[ i ] == 0 ? 1 : 0 ];
                }
            }
        }

        return( ic );
    }

private:
    static const int InterpPoints = 2; ///< The maximal number of points the
        ///< interpolation is based on.
        ///<
    double WFLen2; ///< Window function's Len2 parameter.
        ///<
    double WFFreq; ///< Window function's Freq parameter.
        ///<
    double WFAlpha; ///< Window function's Alpha parameter.
        ///<
    int FracCount; ///< The required number of fractional delay filters.
        ///<
    int Order; ///< The order of the interpolation polynomial.
        ///<
    int Alignment; ///< The required filter table alignment.
        ///<
    int SrcFilterLen; ///< Length of the "source" filters. This is always an
        ///< even value.
        ///<
    int FilterLen; ///< Specifies the number of samples (taps) each fractional
        ///< delay filter has. This is always an even value, adjusted by the
        ///< FltLenAlign.
        ///<
    int FilterSize; ///< The size of a single filter element, equals
        ///< FilterLen * ElementSize.
        ///<
    bool IsInitRequired; ///< "True" if SrcTable filter table initialization
        ///< is required. This value is available only after the call to the
        ///< init() function.
        ///<
    CBuffer< fptype > Table; ///< Interpolation table, size equals to
        ///< ReqFracCount * FilterLen * ElementSize.
        ///<
    CBuffer< uint8_t > TableFillFlags; ///< Contains ReqFracCount + 1
        ///< elements. Bit 0 of every element is 1 if Table already contains
        ///< the filter from SrcTable filtered by ExtFilter. Bit 1 of every
        ///< element means higher order coefficients were filled for the
        ///< filter.
        ///<
    CFltBuffer ExtFilter; ///< External filter that should be applied to every
        ///< fractional delay filter. Can be empty. Half of this filter's
        ///< capacity is used as latency (group delay) value of the filter.
        ///<
    CBuffer< double > SrcTable; ///< Source table of delay filters, contains
        ///< ReqFracCount + 1 elements. This table is used to fill the Table
        ///< with the actual filters, filtered by an external filter.
        ///<
    bool IsSrcTableBuilt; ///< "True" if the SrcTable was built already. This
        ///< variable is set to "false" in the init() function.
        ///<

    /**
     * Function builds source table used in the createFilter() function.
     */

    void buildSrcTable()
    {
        IsSrcTableBuilt = true;
        IsInitRequired = false;

        CDSPPeakedCosineLPF p( WFLen2, WFFreq, WFAlpha );

        const int BufLen = SrcFilterLen * FracCount + InterpPoints - 1;
        const int BufOffs = InterpPoints / 2 - 1;
        const int BufCenter = SrcFilterLen * FracCount / 2 + BufOffs;

        CBuffer< double > Buf( BufLen );
        memset( Buf, 0, ( BufCenter - p.fl2 ) * sizeof( double ));
        int i = BufLen - BufCenter - p.fl2 - 1;
        memset( &Buf[ BufLen - i ], 0, i * sizeof( double ));

        p.generateLPF( &Buf[ BufCenter - p.fl2 ], FracCount );

        SrcTable.alloc(( FracCount + 1 ) * SrcFilterLen );
        TableFillFlags.alloc( FracCount + 1 );
        int j;
        double* op0 = SrcTable;

        for( i = FracCount; i >= 0; i-- )
        {
            TableFillFlags[ i ] = 0;
            double* p = Buf + BufOffs + i;

            for( j = 0; j < SrcFilterLen; j++ )
            {
                op0[ 0 ] = p[ 0 ];
                op0++;
                p += FracCount;
            }
        }

        Table.alloc(( FracCount + 1 ) * FilterSize, Alignment );
    }

    /**
     * Function creates the specified filter in the Table by copying it from
     * the SrcTable and filtering by ExtFilter. Function does nothing if
     * filter was already created.
     *
     * @param k Filter index to create, in the range 0 to FracCount,
     * inclusive.
     */

    void createFilter( const int k )
    {
        if( TableFillFlags[ k ] != 0 )
        {
            return;
        }

        TableFillFlags[ k ] |= 1;
        const int ExtFilterLatency = ExtFilter.getCapacity() / 2;
        const int ResLatency = ExtFilterLatency + SrcFilterLen / 2;
        int ResLen = SrcFilterLen;

        if( ExtFilter.getCapacity() > 0 )
        {
            ResLen += ExtFilter.getCapacity() - 1;
        }

        const int ResOffs = FilterLen / 2 - ResLatency;
        fptype* op = &Table[ k * FilterSize ];
        int i;

        for( i = 0; i < ResOffs; i++ )
        {
            op[ i ] = 0.0;
        }

        for( i = ResOffs + ResLen; i < FilterLen; i++ )
        {
            op[ i ] = 0.0;
        }

        op += ResOffs;
        const double* const srcflt = &SrcTable[ k * SrcFilterLen ];

        if( ExtFilter.getCapacity() == 0 )
        {
            for( i = 0; i < ResLen; i++ )
            {
                op[ i ] = (fptype) srcflt[ i ];
            }

            return;
        }

        // Perform convolution of extflt and srcflt.

        const double* const extflt = &ExtFilter[ 0 ];
        int j;

        for( j = 0; j < ResLen; j++ )
        {
            int k = 0;
            int l = j - ExtFilter.getCapacity() + 1;
            int r = l + ExtFilter.getCapacity();

            if( l < 0 )
            {
                k -= l;
                l = 0;
            }

            if( r > SrcFilterLen )
            {
                r = SrcFilterLen;
            }

            const double* const extfltb = extflt + k;
            const double* const srcfltb = srcflt + l;
            double s = 0.0;
            l = r - l;

            for( i = 0; i < l; i++ )
            {
                s += extfltb[ i ] * srcfltb[ i ];
            }

            op[ j ] = (fptype) s;
        }
    }
};

/**
 * @brief Thread pool for multi-threaded image resizing operation.
 *
 * This base class is used to organize a multi-threaded image resizing
 * operation. The thread pool should consist of threads that initially wait
 * for a signal. Upon receiving a signal (via the startAllWorkloads()
 * function) each previously added thread should execute its workload's
 * process() function once, and return to the wait signal state again. The
 * thread pool should be also able to efficiently wait for all workloads to
 * finish via the waitAllWorkloadsToFinish() function.
 *
 * The image resizing algorithm makes calls to functions of this class.
 */

class CImageResizerThreadPool
{
public:
    CImageResizerThreadPool()
    {
    }

    virtual ~CImageResizerThreadPool()
    {
    }

    /**
     * @brief Thread pool's workload object class.
     *
     * This class should be used as a base class for objects that perform the
     * actual work spread over several threads.
     */

    class CWorkload
    {
    public:
        virtual ~CWorkload()
        {
        }

        /**
         * Function that gets called from the thread when thread pool's
         * startAllWorkloads() function is called.
         */

        virtual void process() = 0;
    };

    /**
     * @return The suggested number of workloads (and their associated
     * threads) to add. The minimal value this function can return is 1. The
     * usual value may depend on the number of physical and virtual cores
     * present in the system, and on other considerations.
     */

    virtual int getSuggestedWorkloadCount() const
    {
        return( 1 );
    }

    /**
     * Function adds a new workload (and possibly thread) to the thread pool.
     * The caller decides how many parallel workloads (and threads) it
     * requires, but this number will not exceed the value returned by the
     * getSuggestedWorkloadCount() function. It is implementation-specific how
     * many workloads to associate with a single thread. But for efficiency
     * reasons each workload should be associated with its own thread.
     *
     * Note that the same set of workload objects will be processed each time
     * the startAllWorkloads() function is called. This means that workload
     * objects are added only once. The caller changes the state of the
     * workload objects and then calls the startAllWorkloads() function to
     * process them.
     *
     * @param Workload Workload object whose process() function will be called
     * from within the thread when the startAllWorkloads() function is called.
     */

    virtual void addWorkload( CWorkload* const Workload )
    {
    }

    /**
     * Function starts all workloads associated with threads previously added
     * via the addWorkload() function. It is assumed that this function
     * performs the necessary "memory barrier" (or "cache sync") kind of
     * operation so that all threads catch up the prior changes made to the
     * workload objects during their wait state.
     */

    virtual void startAllWorkloads()
    {
    }

    /**
     * Function waits for all workloads to finish.
     */

    virtual void waitAllWorkloadsToFinish()
    {
    }

    /**
     * Function removes all workloads previously added via the addWorkload()
     * function. This function gets called only after the
     * waitAllWorkloadsToFinish() function call.
     */

    virtual void removeAllWorkloads()
    {
    }
};

/**
 * @brief Resizing algorithm parameters structure.
 *
 * This structure holds all selectable parameters used by the resizing
 * algorithm at various stages, for both downsizing and upsizing. There are no
 * other parameters exist that can optimize the performance of the resizing
 * algorithm. Filter length parameters can take fractional values.
 *
 * Beside quality, these parameters (except Alpha parameters) directly affect
 * the computative cost of the resizing algorithm. It is possible to trade
 * the visual quality for computative cost.
 *
 * Anti-alias filtering during downsizing can be defined as a considerable
 * reduction of contrast of smallest features of an image. Unfortunately, such
 * de-contrasting partially affects features of all sizes thus producing a
 * non-linearity of frequency response. All pre-defined parameter sets are
 * described by 3 values separated by slashes. The first value is the
 * de-contrasting factor of small features (which are being removed) while
 * the second value is the de-contrasting factor of large features (which
 * should remain intact), with value of 1 equating to "no contrast change".
 * The third value is the optimization score (see below), with value of 0
 * equating to the "perfect" linearity of frequency response.
 *
 * The pre-defined parameter sets offered by this library were auto-optimized
 * for the given LPFltBaseLen, IntFltLen and CorrFltAlpha values. The
 * optimization goal was to minimize the score: the sum of squares of the
 * difference between original and processed images (which was not actually
 * resized, k=1). The original image was a 0.5 megapixel uniformly-distributed
 * white-noise image with pixel intensities in the 0-1 range. Such goal
 * converges very well and produces filtering system with the flattest
 * frequency response possible for the given constraints. With this goal,
 * increasing the LPFltBaseLen value reduces the general amount of aliasing
 * artifacts.
 */

struct CImageResizerParams
{
    double CorrFltAlpha; ///< Alpha parameter of the Peaked Cosine window
        ///< function used on the correction filter. The "usable" values are
        ///< in the narrow range 1.0 to 1.5.
        ///<
    double CorrFltLen; ///< Correction filter's length in samples (taps). The
        ///< "usable" range is narrow, 5.5 to 8, as to minimize the
        ///< "overcorrection" which is mathematically precise, but visually
        ///< unacceptable.
        ///<
    double IntFltAlpha; ///< Alpha parameter of the Peaked Cosine window
        ///< function used on the interpolation low-pass filter. The "usable"
        ///< values are in the range 1.5 to 2.5.
        ///<
    double IntFltCutoff; ///< Interpolation low-pass filter's cutoff frequency
        ///< (normalized, [0; 1]). The "usable" range is 0.6 to 0.8.
        ///<
    double IntFltLen; ///< Interpolation low-pass filter's length in samples
        ///< (taps). The length value should be at least 18 or otherwise a
        ///< "dark grid" artifact will be introduced if a further sharpening
        ///< is applied. IntFltLen together with other IntFlt parameters
        ///< should be tuned in a way that produces the flattest frequency
        ///< response in 0-0.5 normalized frequency range (this range is due
        ///< to 2X upsampling).
        ///<
    double LPFltAlpha; ///< Alpha parameter of the Peaked Cosine window
        ///< function used on the low-pass filter. The "usable" values are
        ///< in the range 1.5 to 6.5.
        ///<
    double LPFltBaseLen; ///< Base length of the low-pass (aka anti-aliasing
        ///< or reconstruction) filter, in samples (taps), further adjusted by
        ///< the actual cutoff frequency, upsampling and downsampling factors.
        ///< The "usable" range is between 6 and 9.
        ///<
    double LPFltCutoffMult; ///< Low-pass filter's cutoff frequency
        ///< multiplier. This value can be both below and above 1.0 as
        ///< low-pass filters are inserted on downsampling and upsampling
        ///< steps and always have corner frequency equal to or below 0.5pi.
        ///< This multiplier shifts low-pass filter's corner frequency towards
        ///< lower (if below 1.0) or higher (if above 1.0) frequencies. This
        ///< multiplier can be way below 1.0 since any additional
        ///< high-frequency damping will be partially corrected by the
        ///< correction filter. The "usable" range is 0.3 to 1.0.
        ///<

    CImageResizerParams()
        : HBFltAlpha( 1.75395 )
        , HBFltCutoff( 0.40356 )
        , HBFltLen( 22.00000 )
    {
    }

    double HBFltAlpha; ///< Half-band filter's Alpha. Assigned internally.
        ///<
    double HBFltCutoff; ///< Half-band filter's cutoff point [0; 1]. Assigned
        ///< internally.
        ///<
    double HBFltLen; ///< Length of the half-band low-pass filter. Assigned
        ///< internally. Internally used to perform 2X or higher downsampling.
        ///< These filter parameters should be treated as "technical" and do
        ///< not require adjustment as they were tuned to suit all
        ///< combinations of other parameters. This half-band filter provides
        ///< a wide transition band (for minimal ringing artifacts) and a high
        ///< stop-band attenuation (for minimal aliasing).
        ///<
};

/**
 * @brief The default set of resizing algorithm parameters
 * (10.01/1.029/0.019169).
 *
 * This is the default set of resizing parameters that was designed to deliver
 * a sharp image while still providing a low amount of ringing artifacts, and
 * having a reasonable computational cost.
 */

struct CImageResizerParamsDef : public CImageResizerParams
{
    CImageResizerParamsDef()
    {
        CorrFltAlpha = 1.0;//10.01/1.88/1.029(522.43)/0.019169:258648,446808
        CorrFltLen = 6.30770;
        IntFltAlpha = 2.27825;
        IntFltCutoff = 0.75493;
        IntFltLen = 18.0;
        LPFltAlpha = 3.40127;
        LPFltBaseLen = 7.78;
        LPFltCutoffMult = 0.78797;
    }
};

/**
 * @brief Set of resizing algorithm parameters for ultra-low-ringing
 * performance (7.69/1.069/0.000245).
 *
 * This set of resizing algorithm parameters offers the lowest amount of
 * ringing this library is capable of providing while still offering a decent
 * quality. Low ringing is attained at the expense of higher aliasing
 * artifacts and a slightly reduced contrast.
 */

struct CImageResizerParamsULR : public CImageResizerParams
{
    CImageResizerParamsULR()
    {
        CorrFltAlpha = 1.0;//7.69/1.97/1.069(31445.45)/0.000245:258627,436845
        CorrFltLen = 5.83280;
        IntFltAlpha = 2.11453;
        IntFltCutoff = 0.73986;
        IntFltLen = 18.0;
        LPFltAlpha = 1.73455;
        LPFltBaseLen = 6.40;
        LPFltCutoffMult = 0.61314;
    }
};

/**
 * @brief Set of resizing algorithm parameters for low-ringing performance
 * (7.86/1.065/0.000106).
 *
 * This set of resizing algorithm parameters offers a very low-ringing
 * performance at the expense of higher aliasing artifacts and a slightly
 * reduced contrast.
 */

struct CImageResizerParamsLR : public CImageResizerParams
{
    CImageResizerParamsLR()
    {
        CorrFltAlpha = 1.0;//7.86/1.96/1.065(73865.02)/0.000106:258636,437381
        CorrFltLen = 5.87671;
        IntFltAlpha = 2.25322;
        IntFltCutoff = 0.74090;
        IntFltLen = 18.0;
        LPFltAlpha = 1.79306;
        LPFltBaseLen = 7.00;
        LPFltCutoffMult = 0.68881;
    }
};

/**
 * @brief Set of resizing algorithm parameters for lower-ringing performance
 * (8.86/1.046/0.010168).
 *
 * This set of resizing algorithm parameters offers a lower-ringing
 * performance in comparison to the default setting, at the expense of higher
 * aliasing artifacts and a slightly reduced contrast.
 */

struct CImageResizerParamsLow : public CImageResizerParams
{
    CImageResizerParamsLow()
    {
        CorrFltAlpha = 1.0;//8.86/1.92/1.046(871.54)/0.010168:258647,442252
        CorrFltLen = 6.09757;
        IntFltAlpha = 2.36704;
        IntFltCutoff = 0.74674;
        IntFltLen = 18.0;
        LPFltAlpha = 2.19427;
        LPFltBaseLen = 7.66;
        LPFltCutoffMult = 0.75380;
    }
};

/**
 * @brief Set of resizing algorithm parameters for low-aliasing
 * resizing (11.81/1.012/0.038379).
 *
 * This set of resizing algorithm parameters offers a considerable
 * anti-aliasing performance with a good frequency response linearity (and
 * contrast). This is an intermediate setting between the default and Ultra
 * parameters.
 */

struct CImageResizerParamsHigh : public CImageResizerParams
{
    CImageResizerParamsHigh()
    {
        CorrFltAlpha = 1.0;//11.81/1.83/1.012(307.84)/0.038379:258660,452719
        CorrFltLen = 6.80909;
        IntFltAlpha = 2.44917;
        IntFltCutoff = 0.75856;
        IntFltLen = 18.0;
        LPFltAlpha = 4.39527;
        LPFltBaseLen = 8.18;
        LPFltCutoffMult = 0.79172;
    }
};

/**
 * @brief Set of resizing algorithm parameters for ultra low-aliasing
 * resizing (13.65/1.001/0.000483).
 *
 * This set of resizing algorithm parameters offers a very considerable
 * anti-aliasing performance with a good frequency response linearity (and
 * contrast). This set of parameters is computationally expensive and may
 * produce ringing artifacts on sharp features.
 */

struct CImageResizerParamsUltra : public CImageResizerParams
{
    CImageResizerParamsUltra()
    {
        CorrFltAlpha = 1.0;//13.65/1.79/1.001(28288.41)/0.000483:258658,457974
        CorrFltLen = 7.48060;
        IntFltAlpha = 1.93750;
        IntFltCutoff = 0.75462;
        IntFltLen = 18.0;
        LPFltAlpha = 5.55209;
        LPFltBaseLen = 8.34;
        LPFltCutoffMult = 0.78002;
    }
};

/**
 * @brief Image resizing variables class.
 *
 * This is an utility "catch all" class that defines various variables used
 * during image resizing. Several variables that are explicitly initialized in
 * this class' constructor are also used as additional "input" variables to
 * the image resizing function. These variables will not be changed by the
 * avir::CImageResizer<>::resizeImage() function.
 */

class CImageResizerVars
{
public:
    int ElCount; ///< The number of "fptype" elements used to store 1 pixel.
        ///<
    int ElCountIO; ///< The number of source and destination image's elements
        ///< used to store 1 pixel.
        ///<
    int fppack; ///< The number of atomic types stored in a single "fptype"
        ///< element.
        ///<
    int fpalign; ///< Suggested alignment size in bytes. This is not a
        ///< required alignment, because image resizing algorithm cannot be
        ///< made to have a strictly aligned data access in all cases (e.g.
        ///< de-interleaved interpolation cannot perform aligned accesses).
        ///<
    int elalign; ///< Length alignment of arrays of elements. This applies to
        ///< filters and intermediate buffers: this constant forces filters
        ///< and scanlines to have a length which is a multiple of this value,
        ///< for more efficient SIMD implementation.
        ///<
    int packmode; ///< 0 if interleaved packing, 1 if de-interleaved.
        ///<
    int BufLen[ 2 ]; ///< Intermediate buffers' lengths in "fptype" elements.
    int BufOffs[ 2 ]; ///< Offsets into the intermediate buffers, used to
        ///< provide prefix elements required during processing so that no
        ///< "out of range" access happens. This offset is a multiple of
        ///< ElCount if pixels are stored in interleaved form.
        ///<
    double k; ///< Resizing step coefficient, updated to reflect the actually
        ///< used coefficient during resizing.
        ///<
    double o; ///< Starting pixel offset inside the source image, updated to
        ///< reflect the actually used offset during resizing.
        ///<
    int ResizeStep; ///< Index of the resizing step in the latest filtering
        ///< steps array.
        ///<
    double InGammaMult; ///< Input gamma multiplier, used to convert input
        ///< data to 0 to 1 range. 0.0 if no gamma is in use.
        ///<
    double OutGammaMult; ///< Output gamma multiplier, used to convert data to
        ///< 0 to 255/65535 range. 0.0 if no gamma is in use.
        ///<

    double ox; ///< Start X pixel offset within source image (can be
        ///< negative). Positive offset moves image to the left.
        ///<
    double oy; ///< Start Y pixel offset within source image (can be
        ///< negative). Positive offset moves image to the top.
        ///<
    CImageResizerThreadPool* ThreadPool; ///< Thread pool to be used by the
        ///< image resizing function. Set to NULL to use single-threaded
        ///< processing.
        ///<
    bool UseSRGBGamma; ///< Perform sRGB gamma linearization (correction).
        ///<
    int BuildMode; ///< The build mode to use, for debugging purposes. Set to
        ///< -1 to select a minimal-complexity mode automatically. All build
        ///< modes deliver similar results with minor deviations.
        ///<
    int RndSeed; ///< Random seed parameter. This parameter may be incremented
        ///< after each random generator initialization. The use of this
        ///< variable depends on the ditherer implementation.
        ///<

    CImageResizerVars()
        : ox( 0.0 )
        , oy( 0.0 )
        , ThreadPool( nullptr )
        , UseSRGBGamma( false )
        , BuildMode( -1 )
        , RndSeed( 0 )
    {
    }
};

/**
 * @brief Image resizer's filtering step class.
 *
 * Class defines data to perform a single filtering step over a whole
 * horizontal or vertical scanline. Resizing consists of 1 or more steps that
 * may be performed before the actual resizing takes place. Filtering may also
 * follow a resizing step. Each step must ensure that scanline data contains
 * enough pixels to perform the next step (which may be resizing) without
 * exceeding scanline's bounds.
 *
 * A derived class must implement several "const" and "static" functions that
 * are used to perform the actual filtering in interleaved or de-interleaved
 * mode.
 *
 * @tparam fptype Floating point type to use for storing pixel elements. SIMD
 * types can be used: in this case each element may hold a whole pixel.
 * @tparam fptypeatom The atomic type the "fptype" consists of.
 */

template< class fptype, class fptypeatom >
class CImageResizerFilterStep
{
public:
    bool IsUpsample; ///< "True" if this step is an upsampling step, "false"
        ///< if downsampling step. Should be set to "false" if ResampleFactor
        ///< equals 0.
        ///<
    int ResampleFactor; ///< Resample factor (>=1). If 0, this is a resizing
        ///< step. This value should be >1 if IsUpsample equals "true".
        ///<
    CBuffer< fptype > Flt; ///< Filter to use at this step.
        ///<
    CFltBuffer FltOrig; ///< Originally-designed filter. This buffer may not
        ///< be assigned. Assigned by filters that precede the resizing step
        ///< if such filter is planned to be embedded into the interpolation
        ///< filter as "external" filter. If IsUpsample=true and this filter
        ///< buffer is not empty, the upsampling step will not itself apply
        ///< any filtering over upsampled input scanline.
        ///<
    double DCGain; ///< DC gain which was applied to the filter. Not defined
        ///< if ResampleFactor = 0.
        ///<
    int FltLatency; ///< Filter's latency (group delay, shift) in pixels.
        ///<
    const CImageResizerVars* Vars; ///< Image resizing-related variables.
        ///<
    int InLen; ///< Input scanline's length in pixels.
        ///<
    int InBuf; ///< Input buffer index, 0 or 1.
        ///<
    int InPrefix; ///< Required input prefix pixels. These prefix pixels will
        ///< be filled with source scanline's first pixel value. If IsUpsample
        ///< is "true", this is the additional number of times the first pixel
        ///< will be filtered before processing scanline, this number is also
        ///< reflected in the OutPrefix.
        ///<
    int InSuffix; ///< Required input suffix pixels. These suffix pixels will
        ///< be filled with source scanline's last pixel value. If IsUpsample
        ///< is "true", this is the additional number of times the last pixel
        ///< will be filtered before processing scanline, this number is also
        ///< reflected in the OutSuffix.
        ///<
    int InElIncr; ///< Pixel element increment within the input buffer, used
        ///< during de-interleaved processing: in this case each image's
        ///< channel is stored independently, InElIncr elements apart.
        ///<
    int OutLen; ///< Length of the resulting scanline.
        ///<
    int OutBuf; ///< Output buffer index. 0 or 1; 2 for the last step.
        ///<
    int OutPrefix; ///< Required output prefix pixels. These prefix pixels
        ///< will not be pre-filled with any values. Value is valid only if
        ///< IsUpsample equals "true".
        ///<
    int OutSuffix; ///< Required input suffix pixels. These suffix pixels will
        ///< not be pre-filled with any values. Value is valid only if
        ///< IsUpsample equals "true".
        ///<
    int OutElIncr; ///< Pixel element increment within the output buffer, used
        ///< during de-interleaved processing. Equals to the InBufElIncr of
        ///< the next step.
        ///<
    CBuffer< fptype > PrefixDC; ///< DC component fluctuations added at the
        ///< start of the resulting scanline, used when IsUpsample equals
        ///< "true".
        ///<
    CBuffer< fptype > SuffixDC; ///< DC component fluctuations added at the
        ///< end of the resulting scanline, used when IsUpsample equals
        ///< "true".
        ///<
    int EdgePixelCount; ///< The number of edge pixels added. Affects the
        ///< initial position within the input scanline, used to produce edge
        ///< pixels. This variable is used and should be defined when
        ///< IsUpsample=false and ResampleFactor>0. When assigning this
        ///< variable it is also necessary to update InPrefix, OutLen and
        ///< Vars.o variables.
        ///<
    static const int EdgePixelCountDef = 3; ///< The default number of pixels
        ///< additionally produced at scanline edges during filtering. This is
        ///< required to reduce edge artifacts.
        ///<

    /**
     * @brief Resizing position structure.
     *
     * Structure holds resizing position and pointer to fractional delay
     * filter.
     */

    struct CResizePos
    {
        int SrcPosInt; ///< Source scanline position.
            ///<
        int fti; ///< Fractional delay filter index.
            ///<
        const fptype* ftp; ///< Fractional delay filter pointer.
            ///<
        fptypeatom x; ///< Interpolation coefficient between delay filters.
            ///<
        int SrcOffs; ///< Source scanline offset.
            ///<
    };

    /**
     * @brief Resizing positions buffer class.
     *
     * This class combines buffer together with variables that define resizing
     * stepping.
     */

    class CRPosBuf : public CBuffer< CResizePos >
    {
    public:
        double k; ///< Resizing step.
            ///<
        double o; ///< Resizing offset.
            ///<
        int FracCount; ///< The number of fractional delay filters in a filter
            ///< bank used together with this buffer.
            ///<
    };

    /**
     * @brief Resizing positions buffer array class.
     *
     * This class combines structure array of the CRPosBuf class objects with
     * the function that locates or creates buffer with the required resizing
     * stepping.
     */

    class CRPosBufArray : public CStructArray< CRPosBuf >
    {
    public:
        using CStructArray< CRPosBuf > :: add;
        using CStructArray< CRPosBuf > :: getItemCount;

        /**
         * Function returns the resizing positions buffer with the required
         * stepping. If no such buffer exists, it is created.
         *
         * @param k Resizing step.
         * @param o Resizing offset.
         * @param FracCount The number of fractional delay filters in a filter
         * bank used together with this buffer.
         * @return Reference to the CRPosBuf object.
         */

        CRPosBuf& getRPosBuf( const double k, const double o,
            const int FracCount )
        {
            int i;

            for( i = 0; i < getItemCount(); i++ )
            {
                CRPosBuf& Buf = (*this)[ i ];

                if( Buf.k == k && Buf.o == o && Buf.FracCount == FracCount )
                {
                    return( Buf );
                }
            }

            CRPosBuf& NewBuf = add();
            NewBuf.k = k;
            NewBuf.o = o;
            NewBuf.FracCount = FracCount;

            return( NewBuf );
        }
    };

    CRPosBuf* RPosBuf; ///< Resizing positions buffer. Used when
        ///< ResampleFactor equals 0 (resizing step).
        ///<
    CDSPFracFilterBankLin< fptype >* FltBank; ///< Filter bank in use by *this
        ///< resizing step.
        ///<
};

/**
 * @brief Interleaved filtering steps implementation class.
 *
 * This class implements scanline filtering functions in interleaved mode.
 * This means that each pixel is processed independently, not in groups.
 *
 * @tparam fptype Floating point type to use for storing pixel elements. SIMD
 * types can be used: in this case each element may hold a whole pixel.
 * @tparam fptypeatom The atomic type the "fptype" consists of.
 */

template< class fptype, class fptypeatom >
class CImageResizerFilterStepINL :
    public CImageResizerFilterStep< fptype, fptypeatom >
{
public:
    using CImageResizerFilterStep< fptype, fptypeatom > :: IsUpsample;
    using CImageResizerFilterStep< fptype, fptypeatom > :: ResampleFactor;
    using CImageResizerFilterStep< fptype, fptypeatom > :: Flt;
    using CImageResizerFilterStep< fptype, fptypeatom > :: FltOrig;
    using CImageResizerFilterStep< fptype, fptypeatom > :: FltLatency;
    using CImageResizerFilterStep< fptype, fptypeatom > :: Vars;
    using CImageResizerFilterStep< fptype, fptypeatom > :: InLen;
    using CImageResizerFilterStep< fptype, fptypeatom > :: InPrefix;
    using CImageResizerFilterStep< fptype, fptypeatom > :: InSuffix;
    using CImageResizerFilterStep< fptype, fptypeatom > :: OutLen;
    using CImageResizerFilterStep< fptype, fptypeatom > :: OutPrefix;
    using CImageResizerFilterStep< fptype, fptypeatom > :: OutSuffix;
    using CImageResizerFilterStep< fptype, fptypeatom > :: PrefixDC;
    using CImageResizerFilterStep< fptype, fptypeatom > :: SuffixDC;
    using CImageResizerFilterStep< fptype, fptypeatom > :: RPosBuf;
    using CImageResizerFilterStep< fptype, fptypeatom > :: FltBank;
    using CImageResizerFilterStep< fptype, fptypeatom > :: EdgePixelCount;

    /**
     * Function performs "packing" of a scanline and type conversion.
     * Scanline, depending on the "fptype" can be potentially stored as a
     * packed SIMD values having a certain atomic type. If required, the sRGB
     * gamma correction is applied.
     *
     * @param ip Input scanline.
     * @param op0 Output scanline.
     * @param l0 The number of pixels to "pack".
     */

    template< class Tin >
    void packScanline( const Tin* ip, fptype* const op0, const int l0 ) const
    {
        const int ElCount = Vars -> ElCount;
        const int ElCountIO = Vars -> ElCountIO;
        fptype* op = op0;
        int l = l0;

        if( !Vars -> UseSRGBGamma )
        {
            if( ElCountIO == 1 )
            {
                while( l > 0 )
                {
                    fptypeatom* v = (fptypeatom*) op;
                    v[ 0 ] = (fptypeatom) ip[ 0 ];
                    op += ElCount;
                    ip++;
                    l--;
                }
            }
            else
            if( ElCountIO == 4 )
            {
                while( l > 0 )
                {
                    fptypeatom* v = (fptypeatom*) op;
                    v[ 0 ] = (fptypeatom) ip[ 0 ];
                    v[ 1 ] = (fptypeatom) ip[ 1 ];
                    v[ 2 ] = (fptypeatom) ip[ 2 ];
                    v[ 3 ] = (fptypeatom) ip[ 3 ];
                    op += ElCount;
                    ip += 4;
                    l--;
                }
            }
            else
            if( ElCountIO == 3 )
            {
                while( l > 0 )
                {
                    fptypeatom* v = (fptypeatom*) op;
                    v[ 0 ] = (fptypeatom) ip[ 0 ];
                    v[ 1 ] = (fptypeatom) ip[ 1 ];
                    v[ 2 ] = (fptypeatom) ip[ 2 ];
                    op += ElCount;
                    ip += 3;
                    l--;
                }
            }
            else
            if( ElCountIO == 2 )
            {
                while( l > 0 )
                {
                    fptypeatom* v = (fptypeatom*) op;
                    v[ 0 ] = (fptypeatom) ip[ 0 ];
                    v[ 1 ] = (fptypeatom) ip[ 1 ];
                    op += ElCount;
                    ip += 2;
                    l--;
                }
            }
        }
        else
        {
            const fptypeatom gm = (fptypeatom) Vars -> InGammaMult;

            if( ElCountIO == 1 )
            {
                while( l > 0 )
                {
                    fptypeatom* v = (fptypeatom*) op;
                    v[ 0 ] = convertSRGB2Lin( (fptypeatom) ip[ 0 ] * gm );
                    op += ElCount;
                    ip++;
                    l--;
                }
            }
            else
            if( ElCountIO == 4 )
            {
                while( l > 0 )
                {
                    fptypeatom* v = (fptypeatom*) op;
                    v[ 0 ] = convertSRGB2Lin( (fptypeatom) ip[ 0 ] * gm );
                    v[ 1 ] = convertSRGB2Lin( (fptypeatom) ip[ 1 ] * gm );
                    v[ 2 ] = convertSRGB2Lin( (fptypeatom) ip[ 2 ] * gm );
                    v[ 3 ] = convertSRGB2Lin( (fptypeatom) ip[ 3 ] * gm );
                    op += ElCount;
                    ip += 4;
                    l--;
                }
            }
            else
            if( ElCountIO == 3 )
            {
                while( l > 0 )
                {
                    fptypeatom* v = (fptypeatom*) op;
                    v[ 0 ] = convertSRGB2Lin( (fptypeatom) ip[ 0 ] * gm );
                    v[ 1 ] = convertSRGB2Lin( (fptypeatom) ip[ 1 ] * gm );
                    v[ 2 ] = convertSRGB2Lin( (fptypeatom) ip[ 2 ] * gm );
                    op += ElCount;
                    ip += 3;
                    l--;
                }
            }
            else
            if( ElCountIO == 2 )
            {
                while( l > 0 )
                {
                    fptypeatom* v = (fptypeatom*) op;
                    v[ 0 ] = convertSRGB2Lin( (fptypeatom) ip[ 0 ] * gm );
                    v[ 1 ] = convertSRGB2Lin( (fptypeatom) ip[ 1 ] * gm );
                    op += ElCount;
                    ip += 2;
                    l--;
                }
            }
        }

        const int ZeroCount = ElCount * Vars -> fppack - ElCountIO;
        op = op0;
        l = l0;

        if( ZeroCount == 1 )
        {
            while( l > 0 )
            {
                fptypeatom* v = (fptypeatom*) op + ElCountIO;
                v[ 0 ] = (fptypeatom) 0;
                op += ElCount;
                l--;
            }
        }
        else
        if( ZeroCount == 2 )
        {
            while( l > 0 )
            {
                fptypeatom* v = (fptypeatom*) op + ElCountIO;
                v[ 0 ] = (fptypeatom) 0;
                v[ 1 ] = (fptypeatom) 0;
                op += ElCount;
                l--;
            }
        }
        else
        if( ZeroCount == 3 )
        {
            while( l > 0 )
            {
                fptypeatom* v = (fptypeatom*) op + ElCountIO;
                v[ 0 ] = (fptypeatom) 0;
                v[ 1 ] = (fptypeatom) 0;
                v[ 2 ] = (fptypeatom) 0;
                op += ElCount;
                l--;
            }
        }
    }

    /**
     * Function applies Linear to sRGB gamma correction to the specified
     * scanline.
     *
     * @param p Scanline.
     * @param l The number of pixels to de-linearize.
     * @param Vars0 Image resizing-related variables.
     */

    static void applySRGBGamma( fptype* p, int l,
        const CImageResizerVars& Vars0 )
    {
        const int ElCount = Vars0.ElCount;
        const int ElCountIO = Vars0.ElCountIO;
        const fptypeatom gm = (fptypeatom) Vars0.OutGammaMult;

        if( ElCountIO == 1 )
        {
            while( l > 0 )
            {
                fptypeatom* v = (fptypeatom*) p;
                v[ 0 ] = convertLin2SRGB( v[ 0 ]) * gm;
                p += ElCount;
                l--;
            }
        }
        else
        if( ElCountIO == 4 )
        {
            while( l > 0 )
            {
                fptypeatom* v = (fptypeatom*) p;
                v[ 0 ] = convertLin2SRGB( v[ 0 ]) * gm;
                v[ 1 ] = convertLin2SRGB( v[ 1 ]) * gm;
                v[ 2 ] = convertLin2SRGB( v[ 2 ]) * gm;
                v[ 3 ] = convertLin2SRGB( v[ 3 ]) * gm;
                p += ElCount;
                l--;
            }
        }
        else
        if( ElCountIO == 3 )
        {
            while( l > 0 )
            {
                fptypeatom* v = (fptypeatom*) p;
                v[ 0 ] = convertLin2SRGB( v[ 0 ]) * gm;
                v[ 1 ] = convertLin2SRGB( v[ 1 ]) * gm;
                v[ 2 ] = convertLin2SRGB( v[ 2 ]) * gm;
                p += ElCount;
                l--;
            }
        }
        else
        if( ElCountIO == 2 )
        {
            while( l > 0 )
            {
                fptypeatom* v = (fptypeatom*) p;
                v[ 0 ] = convertLin2SRGB( v[ 0 ]) * gm;
                v[ 1 ] = convertLin2SRGB( v[ 1 ]) * gm;
                p += ElCount;
                l--;
            }
        }
    }

    /**
     * Function converts vertical scanline to horizontal scanline. This
     * function is called by the image resizer when image is resized
     * vertically. This means that the vertical scanline is stored in the
     * same format produced by the packScanline() and maintained by other
     * filtering functions.
     *
     * @param ip Input vertical scanline.
     * @param op Output buffer (temporary buffer used during resizing).
     * @param SrcLen The number of pixels in the input scanline, also used to
     * calculate input buffer increment.
     * @param SrcIncr Input buffer increment to the next vertical pixel.
     */

    void convertVtoH( const fptype* ip, fptype* op, const int SrcLen,
        const int SrcIncr ) const
    {
        const int ElCount = Vars -> ElCount;
        int j;

        if( ElCount == 1 )
        {
            for( j = 0; j < SrcLen; j++ )
            {
                op[ 0 ] = ip[ 0 ];
                ip += SrcIncr;
                op++;
            }
        }
        else
        if( ElCount == 4 )
        {
            for( j = 0; j < SrcLen; j++ )
            {
                op[ 0 ] = ip[ 0 ];
                op[ 1 ] = ip[ 1 ];
                op[ 2 ] = ip[ 2 ];
                op[ 3 ] = ip[ 3 ];
                ip += SrcIncr;
                op += 4;
            }
        }
        else
        if( ElCount == 3 )
        {
            for( j = 0; j < SrcLen; j++ )
            {
                op[ 0 ] = ip[ 0 ];
                op[ 1 ] = ip[ 1 ];
                op[ 2 ] = ip[ 2 ];
                ip += SrcIncr;
                op += 3;
            }
        }
        else
        if( ElCount == 2 )
        {
            for( j = 0; j < SrcLen; j++ )
            {
                op[ 0 ] = ip[ 0 ];
                op[ 1 ] = ip[ 1 ];
                ip += SrcIncr;
                op += 2;
            }
        }
    }

    /**
     * Function performs "unpacking" of a scanline and type conversion
     * (truncation is used when floating point is converted to integer).
     * Scanline, depending on the "fptype" can be potentially stored as a
     * packed SIMD values having a certain atomic type. The unpacking function
     * assumes that scanline is stored in the style produced by the
     * packScanline() function.
     *
     * @param ip Input scanline.
     * @param op Output scanline.
     * @param l The number of pixels to "unpack".
     * @param Vars0 Image resizing-related variables.
     */

    template< class Tout >
    static void unpackScanline( const fptype* ip, Tout* op, int l,
        const CImageResizerVars& Vars0 )
    {
        const int ElCount = Vars0.ElCount;
        const int ElCountIO = Vars0.ElCountIO;

        if( ElCountIO == 1 )
        {
            while( l > 0 )
            {
                const fptypeatom* v = (const fptypeatom*) ip;
                op[ 0 ] = (Tout) v[ 0 ];
                ip += ElCount;
                op++;
                l--;
            }
        }
        else
        if( ElCountIO == 4 )
        {
            while( l > 0 )
            {
                const fptypeatom* v = (const fptypeatom*) ip;
                op[ 0 ] = (Tout) v[ 0 ];
                op[ 1 ] = (Tout) v[ 1 ];
                op[ 2 ] = (Tout) v[ 2 ];
                op[ 3 ] = (Tout) v[ 3 ];
                ip += ElCount;
                op += 4;
                l--;
            }
        }
        else
        if( ElCountIO == 3 )
        {
            while( l > 0 )
            {
                const fptypeatom* v = (const fptypeatom*) ip;
                op[ 0 ] = (Tout) v[ 0 ];
                op[ 1 ] = (Tout) v[ 1 ];
                op[ 2 ] = (Tout) v[ 2 ];
                ip += ElCount;
                op += 3;
                l--;
            }
        }
        else
        if( ElCountIO == 2 )
        {
            while( l > 0 )
            {
                const fptypeatom* v = (const fptypeatom*) ip;
                op[ 0 ] = (Tout) v[ 0 ];
                op[ 1 ] = (Tout) v[ 1 ];
                ip += ElCount;
                op += 2;
                l--;
            }
        }
    }

    /**
     * Function prepares input scanline buffer for *this filtering step.
     * Left- and right-most pixels are replicated to make sure no buffer
     * overrun happens. Such approach also allows to bypass any pointer
     * range checks.
     *
     * @param Src Source buffer.
     */

    void prepareInBuf( fptype* Src ) const
    {
        if( IsUpsample || InPrefix + InSuffix == 0 )
        {
            return;
        }

        const int ElCount = Vars -> ElCount;
        replicateArray( Src, ElCount, Src - ElCount, InPrefix, -ElCount );

        Src += ( InLen - 1 ) * ElCount;
        replicateArray( Src, ElCount, Src + ElCount, InSuffix, ElCount );
    }

    /**
     * Function peforms scanline upsampling with filtering.
     *
     * @param Src Source scanline buffer (length = this -> InLen). Source
     * scanline increment will be equal to ElCount.
     * @param Dst Destination scanline buffer.
     */

    void doUpsample( const fptype* const Src, fptype* const Dst ) const
    {
        const int ElCount = Vars -> ElCount;
        fptype* op0 = &Dst[ -OutPrefix * ElCount ];
        memset( op0, 0, ( OutPrefix + OutLen + OutSuffix ) * ElCount *
            sizeof( fptype ));

        const fptype* ip = Src;
        const int opstep = ElCount * ResampleFactor;
        int l;

        if( FltOrig.getCapacity() > 0 )
        {
            // Do not perform filtering, only upsample.

            op0 += ( OutPrefix % ResampleFactor ) * ElCount;
            l = OutPrefix / ResampleFactor;

            if( ElCount == 1 )
            {
                while( l > 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0 += opstep;
                    l--;
                }

                l = InLen - 1;

                while( l > 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0 += opstep;
                    ip += ElCount;
                    l--;
                }

                l = OutSuffix / ResampleFactor;

                while( l >= 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0 += opstep;
                    l--;
                }
            }
            else
            if( ElCount == 4 )
            {
                while( l > 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0[ 2 ] = ip[ 2 ];
                    op0[ 3 ] = ip[ 3 ];
                    op0 += opstep;
                    l--;
                }

                l = InLen - 1;

                while( l > 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0[ 2 ] = ip[ 2 ];
                    op0[ 3 ] = ip[ 3 ];
                    op0 += opstep;
                    ip += ElCount;
                    l--;
                }

                l = OutSuffix / ResampleFactor;

                while( l >= 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0[ 2 ] = ip[ 2 ];
                    op0[ 3 ] = ip[ 3 ];
                    op0 += opstep;
                    l--;
                }
            }
            else
            if( ElCount == 3 )
            {
                while( l > 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0[ 2 ] = ip[ 2 ];
                    op0 += opstep;
                    l--;
                }

                l = InLen - 1;

                while( l > 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0[ 2 ] = ip[ 2 ];
                    op0 += opstep;
                    ip += ElCount;
                    l--;
                }

                l = OutSuffix / ResampleFactor;

                while( l >= 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0[ 2 ] = ip[ 2 ];
                    op0 += opstep;
                    l--;
                }
            }
            else
            if( ElCount == 2 )
            {
                while( l > 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0 += opstep;
                    l--;
                }

                l = InLen - 1;

                while( l > 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0 += opstep;
                    ip += ElCount;
                    l--;
                }

                l = OutSuffix / ResampleFactor;

                while( l >= 0 )
                {
                    op0[ 0 ] = ip[ 0 ];
                    op0[ 1 ] = ip[ 1 ];
                    op0 += opstep;
                    l--;
                }
            }

            return;
        }

        const fptype* const f = Flt;
        const int flen = Flt.getCapacity();
        fptype* op;
        int i;

        if( ElCount == 1 )
        {
            l = InPrefix;

            while( l > 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ i ] += f[ i ] * ip[ 0 ];
                }

                op0 += opstep;
                l--;
            }

            l = InLen - 1;

            while( l > 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ i ] += f[ i ] * ip[ 0 ];
                }

                ip += ElCount;
                op0 += opstep;
                l--;
            }

            l = InSuffix;

            while( l >= 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ i ] += f[ i ] * ip[ 0 ];
                }

                op0 += opstep;
                l--;
            }
        }
        else
        if( ElCount == 4 )
        {
            l = InPrefix;

            while( l > 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op[ 2 ] += f[ i ] * ip[ 2 ];
                    op[ 3 ] += f[ i ] * ip[ 3 ];
                    op += 4;
                }

                op0 += opstep;
                l--;
            }

            l = InLen - 1;

            while( l > 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op[ 2 ] += f[ i ] * ip[ 2 ];
                    op[ 3 ] += f[ i ] * ip[ 3 ];
                    op += 4;
                }

                ip += ElCount;
                op0 += opstep;
                l--;
            }

            l = InSuffix;

            while( l >= 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op[ 2 ] += f[ i ] * ip[ 2 ];
                    op[ 3 ] += f[ i ] * ip[ 3 ];
                    op += 4;
                }

                op0 += opstep;
                l--;
            }
        }
        else
        if( ElCount == 3 )
        {
            l = InPrefix;

            while( l > 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op[ 2 ] += f[ i ] * ip[ 2 ];
                    op += 3;
                }

                op0 += opstep;
                l--;
            }

            l = InLen - 1;

            while( l > 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op[ 2 ] += f[ i ] * ip[ 2 ];
                    op += 3;
                }

                ip += ElCount;
                op0 += opstep;
                l--;
            }

            l = InSuffix;

            while( l >= 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op[ 2 ] += f[ i ] * ip[ 2 ];
                    op += 3;
                }

                op0 += opstep;
                l--;
            }
        }
        else
        if( ElCount == 2 )
        {
            l = InPrefix;

            while( l > 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op += 2;
                }

                op0 += opstep;
                l--;
            }

            l = InLen - 1;

            while( l > 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op += 2;
                }

                ip += ElCount;
                op0 += opstep;
                l--;
            }

            l = InSuffix;

            while( l >= 0 )
            {
                op = op0;

                for( i = 0; i < flen; i++ )
                {
                    op[ 0 ] += f[ i ] * ip[ 0 ];
                    op[ 1 ] += f[ i ] * ip[ 1 ];
                    op += 2;
                }

                op0 += opstep;
                l--;
            }
        }

        op = op0;
        const fptype* dc = SuffixDC;
        l = SuffixDC.getCapacity();

        if( ElCount == 1 )
        {
            for( i = 0; i < l; i++ )
            {
                op[ i ] += ip[ 0 ] * dc[ i ];
            }
        }
        else
        if( ElCount == 4 )
        {
            while( l > 0 )
            {
                op[ 0 ] += ip[ 0 ] * dc[ 0 ];
                op[ 1 ] += ip[ 1 ] * dc[ 0 ];
                op[ 2 ] += ip[ 2 ] * dc[ 0 ];
                op[ 3 ] += ip[ 3 ] * dc[ 0 ];
                dc++;
                op += 4;
                l--;
            }
        }
        else
        if( ElCount == 3 )
        {
            while( l > 0 )
            {
                op[ 0 ] += ip[ 0 ] * dc[ 0 ];
                op[ 1 ] += ip[ 1 ] * dc[ 0 ];
                op[ 2 ] += ip[ 2 ] * dc[ 0 ];
                dc++;
                op += 3;
                l--;
            }
        }
        else
        if( ElCount == 2 )
        {
            while( l > 0 )
            {
                op[ 0 ] += ip[ 0 ] * dc[ 0 ];
                op[ 1 ] += ip[ 1 ] * dc[ 0 ];
                dc++;
                op += 2;
                l--;
            }
        }

        ip = Src;
        op = Dst - InPrefix * opstep;
        dc = PrefixDC;
        l = PrefixDC.getCapacity();

        if( ElCount == 1 )
        {
            for( i = 0; i < l; i++ )
            {
                op[ i ] += ip[ 0 ] * dc[ i ];
            }
        }
        else
        if( ElCount == 4 )
        {
            while( l > 0 )
            {
                op[ 0 ] += ip[ 0 ] * dc[ 0 ];
                op[ 1 ] += ip[ 1 ] * dc[ 0 ];
                op[ 2 ] += ip[ 2 ] * dc[ 0 ];
                op[ 3 ] += ip[ 3 ] * dc[ 0 ];
                dc++;
                op += 4;
                l--;
            }
        }
        else
        if( ElCount == 3 )
        {
            while( l > 0 )
            {
                op[ 0 ] += ip[ 0 ] * dc[ 0 ];
                op[ 1 ] += ip[ 1 ] * dc[ 0 ];
                op[ 2 ] += ip[ 2 ] * dc[ 0 ];
                dc++;
                op += 3;
                l--;
            }
        }
        else
        if( ElCount == 2 )
        {
            while( l > 0 )
            {
                op[ 0 ] += ip[ 0 ] * dc[ 0 ];
                op[ 1 ] += ip[ 1 ] * dc[ 0 ];
                dc++;
                op += 2;
                l--;
            }
        }
    }

    /**
     * Function peforms scanline filtering with optional downsampling.
     * Function makes use of the symmetry of the filter.
     *
     * @param Src Source scanline buffer (length = this -> InLen). Source
     * scanline increment will be equal to ElCount.
     * @param Dst Destination scanline buffer.
     * @param DstIncr Destination scanline buffer increment, used for
     * horizontal or vertical scanline stepping.
     */

    void doFilter( const fptype* const Src, fptype* Dst,
        const int DstIncr ) const
    {
        const int ElCount = Vars -> ElCount;
        const fptype* const f = &Flt[ FltLatency ];
        const int flen = FltLatency + 1;
        const int ipstep = ElCount * ResampleFactor;
        const fptype* ip = Src - EdgePixelCount * ipstep;
        const fptype* ip1;
        const fptype* ip2;
        int l = OutLen;
        int i;

        if( ElCount == 1 )
        {
            while( l > 0 )
            {
                fptype s = f[ 0 ] * ip[ 0 ];
                ip1 = ip;
                ip2 = ip;

                for( i = 1; i < flen; i++ )
                {
                    ip1++;
                    ip2--;
                    s += f[ i ] * ( ip1[ 0 ] + ip2[ 0 ]);
                }

                Dst[ 0 ] = s;
                Dst += DstIncr;
                ip += ipstep;
                l--;
            }
        }
        else
        if( ElCount == 4 )
        {
            while( l > 0 )
            {
                fptype s1 = f[ 0 ] * ip[ 0 ];
                fptype s2 = f[ 0 ] * ip[ 1 ];
                fptype s3 = f[ 0 ] * ip[ 2 ];
                fptype s4 = f[ 0 ] * ip[ 3 ];
                ip1 = ip;
                ip2 = ip;

                for( i = 1; i < flen; i++ )
                {
                    ip1 += 4;
                    ip2 -= 4;
                    s1 += f[ i ] * ( ip1[ 0 ] + ip2[ 0 ]);
                    s2 += f[ i ] * ( ip1[ 1 ] + ip2[ 1 ]);
                    s3 += f[ i ] * ( ip1[ 2 ] + ip2[ 2 ]);
                    s4 += f[ i ] * ( ip1[ 3 ] + ip2[ 3 ]);
                }

                Dst[ 0 ] = s1;
                Dst[ 1 ] = s2;
                Dst[ 2 ] = s3;
                Dst[ 3 ] = s4;
                Dst += DstIncr;
                ip += ipstep;
                l--;
            }
        }
        else
        if( ElCount == 3 )
        {
            while( l > 0 )
            {
                fptype s1 = f[ 0 ] * ip[ 0 ];
                fptype s2 = f[ 0 ] * ip[ 1 ];
                fptype s3 = f[ 0 ] * ip[ 2 ];
                ip1 = ip;
                ip2 = ip;

                for( i = 1; i < flen; i++ )
                {
                    ip1 += 3;
                    ip2 -= 3;
                    s1 += f[ i ] * ( ip1[ 0 ] + ip2[ 0 ]);
                    s2 += f[ i ] * ( ip1[ 1 ] + ip2[ 1 ]);
                    s3 += f[ i ] * ( ip1[ 2 ] + ip2[ 2 ]);
                }

                Dst[ 0 ] = s1;
                Dst[ 1 ] = s2;
                Dst[ 2 ] = s3;
                Dst += DstIncr;
                ip += ipstep;
                l--;
            }
        }
        else
        if( ElCount == 2 )
        {
            while( l > 0 )
            {
                fptype s1 = f[ 0 ] * ip[ 0 ];
                fptype s2 = f[ 0 ] * ip[ 1 ];
                ip1 = ip;
                ip2 = ip;

                for( i = 1; i < flen; i++ )
                {
                    ip1 += 2;
                    ip2 -= 2;
                    s1 += f[ i ] * ( ip1[ 0 ] + ip2[ 0 ]);
                    s2 += f[ i ] * ( ip1[ 1 ] + ip2[ 1 ]);
                }

                Dst[ 0 ] = s1;
                Dst[ 1 ] = s2;
                Dst += DstIncr;
                ip += ipstep;
                l--;
            }
        }
    }

    /**
     * Function performs resizing of a single scanline. This function does
     * not "know" about the length of the source scanline buffer. This buffer
     * should be padded with enough pixels so that ( SrcPos - FilterLenD2 ) is
     * always >= 0 and ( SrcPos + ( DstLineLen - 1 ) * k + FilterLenD2 + 1 )
     * does not exceed source scanline's buffer length. SrcLine's increment is
     * assumed to be equal to ElCount.
     *
     * @param SrcLine Source scanline buffer.
     * @param DstLine Destination (resized) scanline buffer.
     * @param DstLineIncr Destination scanline position increment, used for
     * horizontal or vertical scanline stepping.
     * @param xx Temporary buffer, of size FltBank -> getFilterLen(), must be
     * aligned by fpclass :: fpalign.
     */

    void doResize( const fptype* SrcLine, fptype* DstLine,
        const int DstLineIncr, fptype* const ) const
    {
        const int IntFltLen = FltBank -> getFilterLen();
        const int ElCount = Vars -> ElCount;
        const typename CImageResizerFilterStep< fptype, fptypeatom > ::
            CResizePos* rpos = &(*RPosBuf)[ 0 ];

        const typename CImageResizerFilterStep< fptype, fptypeatom > ::
            CResizePos* const rpose = rpos + OutLen;

#define AVIR_RESIZE_PART1 \
            while( rpos < rpose ) \
            { \
                const fptype x = (fptype) rpos -> x; \
                const fptype* const ftp = rpos -> ftp; \
                const fptype* const ftp2 = ftp + IntFltLen; \
                const fptype* Src = SrcLine + rpos -> SrcOffs; \
                int i;

#define AVIR_RESIZE_PART1nx \
            while( rpos < rpose ) \
            { \
                const fptype* const ftp = rpos -> ftp; \
                const fptype* Src = SrcLine + rpos -> SrcOffs; \
                int i;

#define AVIR_RESIZE_PART2 \
                DstLine += DstLineIncr; \
                rpos++; \
            }

        if( FltBank -> getOrder() == 1 )
        {
            if( ElCount == 1 )
            {
                AVIR_RESIZE_PART1

                fptype sum = 0.0;

                for( i = 0; i < IntFltLen; i++ )
                {
                    sum += ( ftp[ i ] + ftp2[ i ] * x ) * Src[ i ];
                }

                DstLine[ 0 ] = sum;

                AVIR_RESIZE_PART2
            }
            else
            if( ElCount == 4 )
            {
                AVIR_RESIZE_PART1

                fptype sum[ 4 ];
                sum[ 0 ] = 0.0;
                sum[ 1 ] = 0.0;
                sum[ 2 ] = 0.0;
                sum[ 3 ] = 0.0;

                for( i = 0; i < IntFltLen; i++ )
                {
                    const fptype xx = ftp[ i ] + ftp2[ i ] * x;
                    sum[ 0 ] += xx * Src[ 0 ];
                    sum[ 1 ] += xx * Src[ 1 ];
                    sum[ 2 ] += xx * Src[ 2 ];
                    sum[ 3 ] += xx * Src[ 3 ];
                    Src += 4;
                }

                DstLine[ 0 ] = sum[ 0 ];
                DstLine[ 1 ] = sum[ 1 ];
                DstLine[ 2 ] = sum[ 2 ];
                DstLine[ 3 ] = sum[ 3 ];

                AVIR_RESIZE_PART2
            }
            else
            if( ElCount == 3 )
            {
                AVIR_RESIZE_PART1

                fptype sum[ 3 ];
                sum[ 0 ] = 0.0;
                sum[ 1 ] = 0.0;
                sum[ 2 ] = 0.0;

                for( i = 0; i < IntFltLen; i++ )
                {
                    const fptype xx = ftp[ i ] + ftp2[ i ] * x;
                    sum[ 0 ] += xx * Src[ 0 ];
                    sum[ 1 ] += xx * Src[ 1 ];
                    sum[ 2 ] += xx * Src[ 2 ];
                    Src += 3;
                }

                DstLine[ 0 ] = sum[ 0 ];
                DstLine[ 1 ] = sum[ 1 ];
                DstLine[ 2 ] = sum[ 2 ];

                AVIR_RESIZE_PART2
            }
            else
            if( ElCount == 2 )
            {
                AVIR_RESIZE_PART1

                fptype sum[ 2 ];
                sum[ 0 ] = 0.0;
                sum[ 1 ] = 0.0;

                for( i = 0; i < IntFltLen; i++ )
                {
                    const fptype xx = ftp[ i ] + ftp2[ i ] * x;
                    sum[ 0 ] += xx * Src[ 0 ];
                    sum[ 1 ] += xx * Src[ 1 ];
                    Src += 2;
                }

                DstLine[ 0 ] = sum[ 0 ];
                DstLine[ 1 ] = sum[ 1 ];

                AVIR_RESIZE_PART2
            }
        }
        else
        {
            if( ElCount == 1 )
            {
                AVIR_RESIZE_PART1nx

                fptype sum = 0.0;

                for( i = 0; i < IntFltLen; i++ )
                {
                    sum += ftp[ i ] * Src[ i ];
                }

                DstLine[ 0 ] = sum;

                AVIR_RESIZE_PART2
            }
            else
            if( ElCount == 4 )
            {
                AVIR_RESIZE_PART1nx

                fptype sum[ 4 ];
                sum[ 0 ] = 0.0;
                sum[ 1 ] = 0.0;
                sum[ 2 ] = 0.0;
                sum[ 3 ] = 0.0;

                for( i = 0; i < IntFltLen; i++ )
                {
                    const fptype xx = ftp[ i ];
                    sum[ 0 ] += xx * Src[ 0 ];
                    sum[ 1 ] += xx * Src[ 1 ];
                    sum[ 2 ] += xx * Src[ 2 ];
                    sum[ 3 ] += xx * Src[ 3 ];
                    Src += 4;
                }

                DstLine[ 0 ] = sum[ 0 ];
                DstLine[ 1 ] = sum[ 1 ];
                DstLine[ 2 ] = sum[ 2 ];
                DstLine[ 3 ] = sum[ 3 ];

                AVIR_RESIZE_PART2
            }
            else
            if( ElCount == 3 )
            {
                AVIR_RESIZE_PART1nx

                fptype sum[ 3 ];
                sum[ 0 ] = 0.0;
                sum[ 1 ] = 0.0;
                sum[ 2 ] = 0.0;

                for( i = 0; i < IntFltLen; i++ )
                {
                    const fptype xx = ftp[ i ];
                    sum[ 0 ] += xx * Src[ 0 ];
                    sum[ 1 ] += xx * Src[ 1 ];
                    sum[ 2 ] += xx * Src[ 2 ];
                    Src += 3;
                }

                DstLine[ 0 ] = sum[ 0 ];
                DstLine[ 1 ] = sum[ 1 ];
                DstLine[ 2 ] = sum[ 2 ];

                AVIR_RESIZE_PART2
            }
            else
            if( ElCount == 2 )
            {
                AVIR_RESIZE_PART1nx

                fptype sum[ 2 ];
                sum[ 0 ] = 0.0;
                sum[ 1 ] = 0.0;

                for( i = 0; i < IntFltLen; i++ )
                {
                    const fptype xx = ftp[ i ];
                    sum[ 0 ] += xx * Src[ 0 ];
                    sum[ 1 ] += xx * Src[ 1 ];
                    Src += 2;
                }

                DstLine[ 0 ] = sum[ 0 ];
                DstLine[ 1 ] = sum[ 1 ];

                AVIR_RESIZE_PART2
            }
        }
    }
#undef AVIR_RESIZE_PART2
#undef AVIR_RESIZE_PART1nx
#undef AVIR_RESIZE_PART1
};

/**
 * @brief Image resizer's default dithering class.
 *
 * This class defines an object that performs rounding, clipping and dithering
 * operations over horizontal scanline pixels before scanline is stored in the
 * output buffer.
 *
 * The ditherer should expect the same storage order of the pixels in a
 * scanline as used in the "filtering step" class. So, a separate ditherer
 * class should be defined for each scanline pixel storage style. The default
 * ditherer implements a simple rounding without dithering: it can be used for
 * an efficient dithering method which can be multi-threaded.
 *
 * @tparam fptype Floating point type to use for storing pixel data. SIMD
 * types can be used.
 */

template< class fptype >
class CImageResizerDithererDefINL
{
public:
    /**
     * Function initializes the ditherer object.
     *
     * @param aLen Scanline length in pixels to process.
     * @param aVars Image resizing-related variables.
     * @param aTrMul Bit-depth truncation multiplier. 1 - no additional
     * truncation.
     * @param aPkOut Peak output value allowed.
     */

    void init( const int aLen, const CImageResizerVars& aVars,
        const double aTrMul, const double aPkOut )
    {
        Len = aLen;
        Vars = &aVars;
        LenE = aLen * Vars -> ElCount;
        TrMul0 = aTrMul;
        PkOut0 = aPkOut;
    }

    /**
     * @return "True" if dithering is recursive relative to scanlines meaning
     * multi-threaded execution is not supported by this dithering method.
     */

    static bool isRecursive()
    {
        return( false );
    }

    /**
     * Function performs rounding and clipping operations.
     *
     * @param ResScanline The buffer containing the final scanline.
     */

    void dither( fptype* const ResScanline ) const
    {
        const fptype c0 = 0.0;
        const fptype PkOut = (fptype) PkOut0;
        int j;

        if( TrMul0 == 1.0 )
        {
            // Optimization - do not perform bit depth truncation.

            for( j = 0; j < LenE; j++ )
            {
                ResScanline[ j ] = clamp( round( ResScanline[ j ]), c0,
                    PkOut );
            }
        }
        else
        {
            const fptype TrMul = (fptype) TrMul0;

            for( j = 0; j < LenE; j++ )
            {
                const fptype z0 = round( ResScanline[ j ] / TrMul ) * TrMul;
                ResScanline[ j ] = clamp( z0, c0, PkOut );
            }
        }
    }

protected:
    int Len; ///< Scanline's length in pixels.
        ///<
    const CImageResizerVars* Vars; ///< Image resizing-related variables.
        ///<
    int LenE; ///< = LenE * ElCount.
        ///<
    double TrMul0; ///< Bit-depth truncation multiplier.
        ///<
    double PkOut0; ///< Peak output value allowed.
        ///<
};

/**
 * @brief Image resizer's error-diffusion dithering class, interleaved mode.
 *
 * This ditherer implements error-diffusion dithering which looks good, and
 * whose results are compressed by PNG well. This implementation uses
 * weighting coefficients obtained via machine optimization and visual
 * evaluation.
 *
 * @tparam fptype Floating point type to use for storing pixel data. SIMD
 * types can be used.
 */

template< class fptype >
class CImageResizerDithererErrdINL :
    public CImageResizerDithererDefINL< fptype >
{
public:
    /**
     * Function initializes the ditherer object.
     *
     * @param aLen Scanline length in pixels to process.
     * @param aVars Image resizing-related variables.
     * @param aTrMul Bit-depth truncation multiplier. 1 - no additional
     * truncation.
     * @param aPkOut Peak output value allowed.
     */

    void init( const int aLen, const CImageResizerVars& aVars,
        const double aTrMul, const double aPkOut )
    {
        CImageResizerDithererDefINL< fptype > :: init( aLen, aVars, aTrMul,
            aPkOut );

        ResScanlineDith0.alloc( LenE + Vars -> ElCount, sizeof( fptype ));
        ResScanlineDith = ResScanlineDith0 + Vars -> ElCount;
        int i;

        for( i = 0; i < LenE + Vars -> ElCount; i++ )
        {
            ResScanlineDith0[ i ] = 0.0;
        }
    }

    static bool isRecursive()
    {
        return( true );
    }

    void dither( fptype* const ResScanline )
    {
        const int ElCount = Vars -> ElCount;
        const fptype c0 = 0.0;
        const fptype TrMul = (fptype) TrMul0;
        const fptype PkOut = (fptype) PkOut0;
        int j;

        for( j = 0; j < LenE; j++ )
        {
            ResScanline[ j ] += ResScanlineDith[ j ];
            ResScanlineDith[ j ] = 0.0;
        }

        for( j = 0; j < LenE - ElCount; j++ )
        {
            // Perform rounding, noise estimation and saturation.

            const fptype z0 = round( ResScanline[ j ] / TrMul ) * TrMul;
            const fptype Noise = ResScanline[ j ] - z0;
            ResScanline[ j ] = clamp( z0, c0, PkOut );

            ResScanline[ j + ElCount ] += Noise * (fptype) 0.364842;
            ResScanlineDith[ j - ElCount ] += Noise * (fptype) 0.207305;
            ResScanlineDith[ j ] += Noise * (fptype) 0.364842;
            ResScanlineDith[ j + ElCount ] += Noise * (fptype) 0.063011;
        }

        while( j < LenE )
        {
            const fptype z0 = round( ResScanline[ j ] / TrMul ) * TrMul;
            const fptype Noise = ResScanline[ j ] - z0;
            ResScanline[ j ] = clamp( z0, c0, PkOut );

            ResScanlineDith[ j - ElCount ] += Noise * (fptype) 0.207305;
            ResScanlineDith[ j ] += Noise * (fptype) 0.364842;
            j++;
        }
    }

protected:
    using CImageResizerDithererDefINL< fptype > :: Len;
    using CImageResizerDithererDefINL< fptype > :: Vars;
    using CImageResizerDithererDefINL< fptype > :: LenE;
    using CImageResizerDithererDefINL< fptype > :: TrMul0;
    using CImageResizerDithererDefINL< fptype > :: PkOut0;

    CBuffer< fptype > ResScanlineDith0; ///< Error diffusion buffer.
        ///<
    fptype* ResScanlineDith; ///< Error diffusion buffer pointer which skips
        ///< the first ElCount elements.
        ///<
};

/**
 * @brief Floating-point processing definition and abstraction class.
 *
 * This class defines several constants and typedefs that point to classes
 * that should be used by the image resizing algorithm. Such "definition
 * class" can be used to define alternative scanline processing algorithms
 * (e.g. SIMD) and image scanline packing styles used during processing. This
 * class also offers an abstraction layer for dithering, rounding and
 * clamping (saturation) operation.
 *
 * The fpclass_def class can be used to define processing using both SIMD and
 * non-SIMD types, but using algorithms that are operate on interleaved pixels
 * and non-SIMD optimized themselves.
 *
 * @tparam afptype Floating point type to use for storing intermediate data
 * and variables. For variables that are not used in intensive calculations
 * the "double" type is always used. On the latest Intel processors (like
 * i7-4770K) there is almost no performance difference between "double" and
 * "float". Image quality differences between "double" and "float" are not
 * apparent on 8-bit images. At the same time the "float" uses half amount of
 * working memory the "double" type uses. SIMD types can be used. The
 * functions round() and clamp() in the "avir" or other visible namespace
 * should be available for the specified type. SIMD types allow to perform
 * resizing of images with more than 4 channels, to be exact 4 * SIMD element
 * number (e.g. 16 for float4), without modification of the image resizing
 * algorithm required.
 * @tparam afptypeatom The atomic type the "afptype" consists of.
 * @tparam adith Ditherer class to use during processing.
 */

template< class afptype, class afptypeatom = afptype,
    class adith = CImageResizerDithererDefINL< afptype > >
class fpclass_def
{
public:
    typedef afptype fptype; ///< Floating-point type to use during processing.
        ///<
    typedef afptypeatom fptypeatom; ///< Atomic type "fptype" consists of.
        ///<
    static const int fppack = sizeof( fptype ) / sizeof( fptypeatom ); ///<
        ///< The number of atomic types stored in a single "fptype" element.
        ///<
    static const int fpalign = sizeof( fptype ); ///< Suggested alignment size
        ///< in bytes. This is not a required alignment, because image
        ///< resizing algorithm cannot be made to have a strictly aligned data
        ///< access at all steps (e.g. interpolation cannot perform aligned
        ///< accesses).
        ///<
    static const int elalign = 1; ///< Length alignment of arrays of elements.
        ///< This applies to filters and intermediate buffers: this constant
        ///< forces filters and scanlines to have a length which is a multiple
        ///< of this value, for more efficient SIMD implementation.
        ///<
    static const int packmode = 0; ///< 0 if interleaved packing, 1 if
        ///< de-interleaved.
        ///<
    typedef CImageResizerFilterStepINL< fptype, fptypeatom > CFilterStep; ///<
        ///< Filtering step class to use during processing.
        ///<
    typedef adith CDitherer; ///< Ditherer class to use during processing.
        ///<
};

/**
 * @brief Image resizer class.
 *
 * The object of this class can be used to resize 1-4 channel images to any
 * required size. Resizing is performed by utilizing interpolated sinc
 * fractional delay filters plus (if necessary) a cascade of built-in
 * sinc function-based 2X upsampling or 2X downsampling stages, followed by a
 * correction filtering.
 *
 * Object of this class can be allocated on stack.
 *
 * @tparam fpclass Floating-point processing definition class to use. See
 * avir::fpclass_def for more details.
 */

template< class fpclass = fpclass_def< float > >
class CImageResizer
{
public:
    /**
     * Constructor initializes the resizer.
     *
     * @param aResBitDepth Required bit depth of resulting image (1-16). If
     * integer value output is used (e.g. uint8_t), the bit depth also affects
     * rounding: for example, if aResBitDepth=6 and "Tout" is uint8_t, the
     * result will be rounded to 6 most significant bits (2 least significant
     * bits truncated, with dithering applied).
     * @param aSrcBitDepth Source image's real bit-depth. Set to 0 to use
     * aResBitDepth.
     * @param aParams Resizing algorithm's parameters to use. Leave out for
     * default values. Can be useful when performing automatic optimization of
     * parameters.
     */

    CImageResizer( const int aResBitDepth = 8, const int aSrcBitDepth = 0,
        const CImageResizerParams& aParams = CImageResizerParamsDef() )
        : Params( aParams )
        , ResBitDepth( aResBitDepth )
    {
        SrcBitDepth = ( aSrcBitDepth == 0 ? ResBitDepth : aSrcBitDepth );

        initFilterBank( FixedFilterBank, 1.0, false, CFltBuffer() );
        FixedFilterBank.createAllFilters();
    }

    /**
     * Function resizes image.
     *
     * @param SrcBuf Source image buffer.
     * @param SrcWidth Source image width.
     * @param SrcHeight Source image height.
     * @param SrcScanlineSize Physical size of source scanline in elements
     * (not bytes). If this value is below 1, SrcWidth * ElCountIO will be
     * used as the physical source scanline size.
     * @param[out] NewBuf Buffer to accept the resized image. Can be equal to
     * SrcBuf if the size of the resized image is smaller or equal to source
     * image in size.
     * @param NewWidth New image width.
     * @param NewHeight New image height.
     * @param ElCountIO The number of elements (channels) used to store each
     * source and destination pixel (1-4).
     * @param k Resizing step (one output pixel corresponds to "k" input
     * pixels). A downsizing factor if > 1.0; upsizing factor if <= 1.0.
     * Multiply by -1 if you would like to bypass "ox" and "oy" adjustment
     * which is done by default to produce a centered image. If step value
     * equals 0, the step value will be chosen automatically and independently
     * for horizontal and vertical resizing.
     * @param[in,out] aVars Pointer to variables structure to be passed to the
     * image resizing function. Can be NULL. Only variables that are
     * initialized in default constructor of this structure are accepted by
     * this function. These variables will not be changed by this function.
     * All other variables can be modified by this function. The access to
     * this object is not thread-safe, each concurrent instance of this
     * function should use a separate aVars object.
     * @tparam Tin Input buffer element's type. Can be uint8_t (0-255 value
     * range), uint16_t (0-65535 value range), float (0.0-1.0 value range),
     * double (0.0-1.0 value range). Larger integer types are treated as
     * uint16_t. Signed integer types are unsupported.
     * @tparam Tout Output buffer element's type. Can be uint8_t (0-255 value
     * range), uint16_t (0-65535 value range), float (0.0-1.0 value range),
     * double (0.0-1.0 value range). Larger integer types are treated as
     * uint16_t. Signed integer types are unsupported.
     */

    template< class Tin, class Tout >
    void resizeImage( const Tin* const SrcBuf, const int SrcWidth,
        const int SrcHeight, int SrcScanlineSize, Tout* const NewBuf,
        const int NewWidth, const int NewHeight, const int ElCountIO,
        const double k, CImageResizerVars* const aVars = nullptr ) const
    {
        if( SrcWidth == 0 || SrcHeight == 0 )
        {
            memset( NewBuf, 0, (size_t) NewWidth * NewHeight *
                sizeof( Tout ));

            return;
        }
        else
        if( NewWidth == 0 || NewHeight == 0 )
        {
            return;
        }

        CImageResizerVars DefVars;
        CImageResizerVars& Vars = ( aVars == nullptr ? DefVars : *aVars );

        CImageResizerThreadPool DefThreadPool;
        CImageResizerThreadPool& ThreadPool = ( Vars.ThreadPool == nullptr ?
            DefThreadPool : *Vars.ThreadPool );

        // Define resizing steps, also optionally modify offsets so that
        // resizing produces a "centered" image.

        double kx;
        double ky;
        double ox = Vars.ox;
        double oy = Vars.oy;

        if( k == 0.0 )
        {
            if( NewWidth > SrcWidth )
            {
                kx = (double) ( SrcWidth - 1 ) / ( NewWidth - 1 );
            }
            else
            {
                kx = (double) SrcWidth / NewWidth;
                ox += ( kx - 1.0 ) * 0.5;
            }

            if( NewHeight > SrcHeight )
            {
                ky = (double) ( SrcHeight - 1 ) / ( NewHeight - 1 );
            }
            else
            {
                ky = (double) SrcHeight / NewHeight;
                oy += ( ky - 1.0 ) * 0.5;
            }
        }
        else
        if( k > 0.0 )
        {
            kx = k;
            ky = k;

            if( k > 1.0 )
            {
                const double ko = ( k - 1.0 ) * 0.5;
                ox += ko;
                oy += ko;
            }
        }
        else
        {
            kx = -k;
            ky = -k;
        }

        // Evaluate pre-multipliers used on the output stage.

        const bool IsInFloat = ( (Tin) 0.4 != 0 );
        const bool IsOutFloat = ( (Tout) 0.4 != 0 );
        double OutMul; // Output multiplier.

        if( Vars.UseSRGBGamma )
        {
            if( IsInFloat )
            {
                Vars.InGammaMult = 1.0;
            }
            else
            {
                Vars.InGammaMult =
                    1.0 / ( sizeof( Tin ) == 1 ? 255.0 : 65535.0 );
            }

            if( IsOutFloat )
            {
                Vars.OutGammaMult = 1.0;
            }
            else
            {
                Vars.OutGammaMult = ( sizeof( Tout ) == 1 ? 255.0 : 65535.0 );
            }

            OutMul = 1.0;
        }
        else
        {
            if( IsOutFloat )
            {
                OutMul = 1.0;
            }
            else
            {
                OutMul = ( sizeof( Tout ) == 1 ? 255.0 : 65535.0 );
            }

            if( !IsInFloat )
            {
                OutMul /= ( sizeof( Tin ) == 1 ? 255.0 : 65535.0 );
            }
        }

        // Fill widely-used variables.

        const int ElCount = ( ElCountIO + fpclass :: fppack - 1 ) /
            fpclass :: fppack;

        const int NewWidthE = NewWidth * ElCount;

        if( SrcScanlineSize < 1 )
        {
            SrcScanlineSize = SrcWidth * ElCountIO;
        }

        Vars.ElCount = ElCount;
        Vars.ElCountIO = ElCountIO;
        Vars.fppack = fpclass :: fppack;
        Vars.fpalign = fpclass :: fpalign;
        Vars.elalign = fpclass :: elalign;
        Vars.packmode = fpclass :: packmode;

        // Horizontal scanline filtering and resizing.

        CDSPFracFilterBankLin< fptype > FltBank;
        CFilterSteps FltSteps;
        typename CFilterStep :: CRPosBufArray RPosBufArray;
        CBuffer< uint8_t > UsedFracMap;

        // Perform the filtering steps modeling at various modes, find the
        // most efficient mode for both horizontal and vertical resizing.

        int UseBuildMode = 1;
        const int BuildModeCount =
            ( FixedFilterBank.getOrder() == 0 ? 4 : 2 );

        int m;

        if( Vars.BuildMode >= 0 )
        {
            UseBuildMode = Vars.BuildMode;
        }
        else
        {
            int BestScore = 0x7FFFFFFF;

            for( m = 0; m < BuildModeCount; m++ )
            {
                CDSPFracFilterBankLin< fptype > TmpBank;
                CFilterSteps TmpSteps;
                Vars.k = kx;
                Vars.o = ox;
                buildFilterSteps( TmpSteps, Vars, TmpBank, OutMul, m, true );
                updateFilterStepBuffers( TmpSteps, Vars, RPosBufArray,
                    SrcWidth, NewWidth );

                fillUsedFracMap( TmpSteps[ Vars.ResizeStep ], UsedFracMap );
                const int c = calcComplexity( TmpSteps, Vars, UsedFracMap,
                    SrcHeight );

                if( c < BestScore )
                {
                    UseBuildMode = m;
                    BestScore = c;
                }
            }
        }

        // Perform the actual filtering steps building.

        Vars.k = kx;
        Vars.o = ox;
        buildFilterSteps( FltSteps, Vars, FltBank, OutMul, UseBuildMode,
            false );

        updateFilterStepBuffers( FltSteps, Vars, RPosBufArray, SrcWidth,
            NewWidth );

        updateBufLenAndRPosPtrs( FltSteps, Vars, NewWidth );

        const int ThreadCount = ThreadPool.getSuggestedWorkloadCount();
            // Includes the current thread.

        CStructArray< CThreadData< Tin, Tout > > td;
        td.setItemCount( ThreadCount );
        int i;

        for( i = 0; i < ThreadCount; i++ )
        {
            if( i > 0 )
            {
                ThreadPool.addWorkload( &td[ i ]);
            }

            td[ i ].init( i, ThreadCount, FltSteps, Vars );

            td[ i ].initScanlineQueue( td[ i ].sopResizeH, SrcHeight,
                SrcWidth );
        }

        CBuffer< fptype, size_t > FltBuf( (size_t) NewWidthE * SrcHeight,
            fpclass :: fpalign ); // Temporary buffer that receives
            // horizontally-filtered and resized image.

        for( i = 0; i < SrcHeight; i++ )
        {
            td[ i % ThreadCount ].addScanlineToQueue(
                (void*) &SrcBuf[ (size_t) i * SrcScanlineSize ],
                &FltBuf[ (size_t) i * NewWidthE ]);
        }

        ThreadPool.startAllWorkloads();
        td[ 0 ].processScanlineQueue();
        ThreadPool.waitAllWorkloadsToFinish();

        // Vertical scanline filtering and resizing, reuse previously defined
        // filtering steps if possible.

        const int PrevUseBuildMode = UseBuildMode;

        if( Vars.BuildMode >= 0 )
        {
            UseBuildMode = Vars.BuildMode;
        }
        else
        {
            CImageResizerVars TmpVars( Vars );
            int BestScore = 0x7FFFFFFF;

            for( m = 0; m < BuildModeCount; m++ )
            {
                CDSPFracFilterBankLin< fptype > TmpBank;
                TmpBank.copyInitParams( FltBank );
                CFilterSteps TmpSteps;
                TmpVars.k = ky;
                TmpVars.o = oy;
                buildFilterSteps( TmpSteps, TmpVars, TmpBank, 1.0, m, true );
                updateFilterStepBuffers( TmpSteps, TmpVars, RPosBufArray,
                    SrcHeight, NewHeight );

                fillUsedFracMap( TmpSteps[ TmpVars.ResizeStep ],
                    UsedFracMap );

                const int c = calcComplexity( TmpSteps, TmpVars, UsedFracMap,
                    NewWidth );

                if( c < BestScore )
                {
                    UseBuildMode = m;
                    BestScore = c;
                }
            }
        }

        Vars.k = ky;
        Vars.o = oy;

        if( UseBuildMode == PrevUseBuildMode && ky == kx )
        {
            if( OutMul != 1.0 )
            {
                modifyCorrFilterDCGain( FltSteps, 1.0 / OutMul );
            }
        }
        else
        {
            buildFilterSteps( FltSteps, Vars, FltBank, 1.0, UseBuildMode,
                false );
        }

        updateFilterStepBuffers( FltSteps, Vars, RPosBufArray, SrcHeight,
            NewHeight );

        updateBufLenAndRPosPtrs( FltSteps, Vars, NewWidth );

        if( IsOutFloat && sizeof( FltBuf[ 0 ]) == sizeof( Tout ) &&
            fpclass :: packmode == 0 )
        {
            // In-place output.

            for( i = 0; i < ThreadCount; i++ )
            {
                td[ i ].initScanlineQueue( td[ i ].sopResizeV, NewWidth,
                    SrcHeight, NewWidthE, NewWidthE );
            }

            for( i = 0; i < NewWidth; i++ )
            {
                td[ i % ThreadCount ].addScanlineToQueue(
                    &FltBuf[ (size_t) i * ElCount ],
                    (fptype*) (void*) &NewBuf[ (size_t) i * ElCount ]);
            }

            ThreadPool.startAllWorkloads();
            td[ 0 ].processScanlineQueue();
            ThreadPool.waitAllWorkloadsToFinish();
            ThreadPool.removeAllWorkloads();

            return;
        }

        CBuffer< fptype, size_t > ResBuf( (size_t) NewWidthE * NewHeight,
            fpclass :: fpalign );

        for( i = 0; i < ThreadCount; i++ )
        {
            td[ i ].initScanlineQueue( td[ i ].sopResizeV, NewWidth,
                SrcHeight, NewWidthE, NewWidthE );
        }

        const int im = ( fpclass :: packmode == 0 ? ElCount : 1 );

        for( i = 0; i < NewWidth; i++ )
        {
            td[ i % ThreadCount ].addScanlineToQueue(
                &FltBuf[ (size_t) i * im ], &ResBuf[ (size_t) i * im ]);
        }

        ThreadPool.startAllWorkloads();
        td[ 0 ].processScanlineQueue();
        ThreadPool.waitAllWorkloadsToFinish();

        if( IsOutFloat )
        {
            // Perform output, but skip dithering.

            for( i = 0; i < ThreadCount; i++ )
            {
                td[ i ].initScanlineQueue( td[ i ].sopUnpackH,
                    NewHeight, NewWidth );
            }

            for( i = 0; i < NewHeight; i++ )
            {
                td[ i % ThreadCount ].addScanlineToQueue(
                    &ResBuf[ (size_t) i * NewWidthE ],
                    &NewBuf[ (size_t) i * NewWidth * ElCountIO ]);
            }

            ThreadPool.startAllWorkloads();
            td[ 0 ].processScanlineQueue();
            ThreadPool.waitAllWorkloadsToFinish();
            ThreadPool.removeAllWorkloads();

            return;
        }

        // Perform output with dithering (for integer output only).

        int TruncBits; // The number of lower bits to truncate and dither.
        int OutRange; // Output range.

        if( sizeof( Tout ) == 1 )
        {
            TruncBits = 8 - ResBitDepth;
            OutRange = 255;
        }
        else
        {
            TruncBits = 16 - ResBitDepth;
            OutRange = 65535;
        }

        const double PkOut = OutRange;
        const double TrMul = ( TruncBits > 0 ?
            PkOut / ( OutRange >> TruncBits ) : 1.0 );

        if( CDitherer :: isRecursive() )
        {
            td[ 0 ].getDitherer().init( NewWidth, Vars, TrMul, PkOut );

            if( Vars.UseSRGBGamma )
            {
                for( i = 0; i < NewHeight; i++ )
                {
                    fptype* const ResScanline =
                        &ResBuf[ (size_t) i * NewWidthE ];

                    CFilterStep :: applySRGBGamma( ResScanline, NewWidth,
                        Vars );

                    td[ 0 ].getDitherer().dither( ResScanline );

                    CFilterStep :: unpackScanline( ResScanline,
                        &NewBuf[ (size_t) i * NewWidth * ElCountIO ],
                        NewWidth, Vars );
                }
            }
            else
            {
                for( i = 0; i < NewHeight; i++ )
                {
                    fptype* const ResScanline =
                        &ResBuf[ (size_t) i * NewWidthE ];

                    td[ 0 ].getDitherer().dither( ResScanline );

                    CFilterStep :: unpackScanline( ResScanline,
                        &NewBuf[ (size_t) i * NewWidth * ElCountIO ],
                        NewWidth, Vars );
                }
            }
        }
        else
        {
            for( i = 0; i < ThreadCount; i++ )
            {
                td[ i ].initScanlineQueue( td[ i ].sopDitherAndUnpackH,
                    NewHeight, NewWidth );

                td[ i ].getDitherer().init( NewWidth, Vars, TrMul, PkOut );
            }

            for( i = 0; i < NewHeight; i++ )
            {
                td[ i % ThreadCount ].addScanlineToQueue(
                    &ResBuf[ (size_t) i * NewWidthE ],
                    &NewBuf[ (size_t) i * NewWidth * ElCountIO ]);
            }

            ThreadPool.startAllWorkloads();
            td[ 0 ].processScanlineQueue();
            ThreadPool.waitAllWorkloadsToFinish();
        }

        ThreadPool.removeAllWorkloads();
    }

private:
    typedef typename fpclass :: fptype fptype; ///< Floating-point type to use
        ///< during processing.
        ///<
    typedef typename fpclass :: CFilterStep CFilterStep; ///< Filtering step
        ///< class to use during processing.
        ///<
    typedef typename fpclass :: CDitherer CDitherer; ///< Ditherer class to
        ///< use during processing.
        ///<
    CImageResizerParams Params; ///< Algorithm's parameters currently in use.
        ///<
    int SrcBitDepth; ///< Bit resolution of the source image.
        ///<
    int ResBitDepth; ///< Bit resolution of the resulting image.
        ///<
    CDSPFracFilterBankLin< fptype > FixedFilterBank; ///< Fractional delay
        ///< filter bank with fixed characteristics, mainly for upsizing
        ///< cases.
        ///<

    /**
     * @brief Filtering steps array.
     *
     * The object of this class stores filtering steps together.
     */

    typedef CStructArray< CFilterStep > CFilterSteps;

    /**
     * Function initializes the filter bank in the specified resizing step
     * according to the source and resulting image bit depths.
     *
     * @param FltBank Filter bank to initialize.
     * @param CutoffMult Cutoff multiplier, 0 to 1. 1 corresponds to 0.5pi
     * cutoff point.
     * @param ForceHiOrder "True" if a high-order interpolation should be
     * forced which requires considerably less resources for initialization.
     * @param ExtFilter External filter to apply to interpolation filter.
     */

    void initFilterBank( CDSPFracFilterBankLin< fptype >& FltBank,
        const double CutoffMult, const bool ForceHiOrder,
        const CFltBuffer& ExtFilter ) const
    {
        const int IntBitDepth = ( ResBitDepth > SrcBitDepth ? ResBitDepth :
            SrcBitDepth );

        const double SNR = -6.02 * ( IntBitDepth + 3 );
        int UseOrder;
        int FracCount; // The number of fractional delay filters sampled by
            // the filter bank. This variable affects the signal-to-noise
            // ratio at interpolation stage. Theoretically, at UseOrder==1,
            // 8-bit image resizing requires 66.2 dB SNR or 11. 16-bit
            // resizing requires 114.4 dB SNR or 150. At UseOrder=0 the
            // required number of filters is exponentially higher.

        if( ForceHiOrder || IntBitDepth > 8 )
        {
            UseOrder = 1; // -146 dB max
            FracCount = (int) ceil( 0.23134052 * exp( -0.058062929 * SNR ));
        }
        else
        {
            UseOrder = 0; // -72 dB max
            FracCount = (int) ceil( 0.33287686 * exp( -0.11334583 * SNR ));
        }

        if( FracCount < 2 )
        {
            FracCount = 2;
        }

        FltBank.init( FracCount, UseOrder, Params.IntFltLen / CutoffMult,
            Params.IntFltCutoff * CutoffMult, Params.IntFltAlpha, ExtFilter,
            fpclass :: fpalign, fpclass :: elalign );
    }

    /**
     * Function allocates filter buffer taking "fpclass" alignments into
     * account. The allocated buffer may be larger than the requested size: in
     * this case the additional elements will be zeroed by this function.
     *
     * @param Flt Filter buffer.
     * @param ReqCapacity The required filter buffer's capacity.
     * @param IsModel "True" if filtering steps modeling is performed without
     * actual filter allocation.
     * @param FltExt If non-NULL this variable will receive the number of
     * elements the filter was extended by.
     */

    static void allocFilter( CBuffer< fptype >& Flt, const int ReqCapacity,
        const bool IsModel = false, int* const FltExt = nullptr )
    {
        int UseCapacity = ( ReqCapacity + fpclass :: elalign - 1 ) &
            ~( fpclass :: elalign - 1 );

        int Ext = UseCapacity - ReqCapacity;

        if( FltExt != nullptr )
        {
            *FltExt = Ext;
        }

        if( IsModel )
        {
            Flt.forceCapacity( UseCapacity );
            return;
        }

        Flt.alloc( UseCapacity, fpclass :: fpalign );

        while( Ext > 0 )
        {
            Ext--;
            Flt[ ReqCapacity + Ext ] = 0.0;
        }
    }

    /**
     * Function assigns filter parameters to the specified filtering step
     * object.
     *
     * @param fs Filtering step to assign parameter to. This step cannot be
     * the last step if ResampleFactor greater than 1 was specified.
     * @param IsUpsample "True" if upsampling step. Should be set to "false"
     * if FltCutoff is negative.
     * @param ResampleFactor Resampling factor of this filter (>=1).
     * @param FltCutoff Filter cutoff point. This value will be divided by the
     * ResampleFactor if IsUpsample equals "true". If zero value was
     * specified, the "half-band" predefined filter will be created. In this
     * case the ResampleFactor will modify the filter cutoff point.
     * @param DCGain DC gain to apply to the filter. Assigned to filtering
     * step's DCGain variable.
     * @param UseFltOrig "True" if the originally-designed filter should be
     * left in filtering step's FltOrig buffer. Otherwise it will be freed.
     * @param IsModel "True" if filtering steps modeling is performed without
     * actual filter building.
     */

    void assignFilterParams( CFilterStep& fs, const bool IsUpsample,
        const int ResampleFactor, const double FltCutoff, const double DCGain,
        const bool UseFltOrig, const bool IsModel ) const
    {
        double FltAlpha;
        double Len2;
        double Freq;

        if( FltCutoff == 0.0 )
        {
            const double m = 2.0 / ResampleFactor;
            FltAlpha = Params.HBFltAlpha;
            Len2 = 0.5 * Params.HBFltLen / m;
            Freq = AVIR_PI * Params.HBFltCutoff * m;
        }
        else
        {
            FltAlpha = Params.LPFltAlpha;
            Len2 = 0.25 * Params.LPFltBaseLen / FltCutoff;
            Freq = AVIR_PI * Params.LPFltCutoffMult * FltCutoff;
        }

        if( IsUpsample )
        {
            Len2 *= ResampleFactor;
            Freq /= ResampleFactor;
            fs.DCGain = DCGain * ResampleFactor;
        }
        else
        {
            fs.DCGain = DCGain;
        }

        fs.FltOrig.Len2 = Len2;
        fs.FltOrig.Freq = Freq;
        fs.FltOrig.Alpha = FltAlpha;
        fs.FltOrig.DCGain = fs.DCGain;

        CDSPPeakedCosineLPF w( Len2, Freq, FltAlpha );

        fs.IsUpsample = IsUpsample;
        fs.ResampleFactor = ResampleFactor;
        fs.FltLatency = w.fl2;

        int FltExt; // Filter's extension due to fpclass :: elalign.

        if( IsModel )
        {
            allocFilter( fs.Flt, w.FilterLen, true, &FltExt );

            if( UseFltOrig )
            {
                // Allocate a real buffer even in modeling mode since this
                // filter may be copied by the filter bank.

                fs.FltOrig.alloc( w.FilterLen );
                memset( &fs.FltOrig[ 0 ], 0,
                    w.FilterLen * sizeof( fs.FltOrig[ 0 ]));
            }
        }
        else
        {
            fs.FltOrig.alloc( w.FilterLen );

            w.generateLPF( &fs.FltOrig[ 0 ], 1.0 );
            optimizeFIRFilter( fs.FltOrig, fs.FltLatency );
            normalizeFIRFilter( &fs.FltOrig[ 0 ], fs.FltOrig.getCapacity(),
                fs.DCGain );

            allocFilter( fs.Flt, fs.FltOrig.getCapacity(), false, &FltExt );
            copyArray( &fs.FltOrig[ 0 ], &fs.Flt[ 0 ],
                fs.FltOrig.getCapacity() );

            if( !UseFltOrig )
            {
                fs.FltOrig.free();
            }
        }

        if( IsUpsample )
        {
            int l = fs.Flt.getCapacity() - fs.FltLatency - ResampleFactor -
                FltExt;

            allocFilter( fs.PrefixDC, l, IsModel );
            allocFilter( fs.SuffixDC, fs.FltLatency, IsModel );

            if( IsModel )
            {
                return;
            }

            // Create prefix and suffix "tails" used during upsampling.

            const fptype* ip = &fs.Flt[ fs.FltLatency + ResampleFactor ];
            copyArray( ip, &fs.PrefixDC[ 0 ], l );

            while( true )
            {
                ip += ResampleFactor;
                l -= ResampleFactor;

                if( l <= 0 )
                {
                    break;
                }

                addArray( ip, &fs.PrefixDC[ 0 ], l );
            }

            l = fs.FltLatency;
            fptype* op = &fs.SuffixDC[ 0 ];
            copyArray( &fs.Flt[ 0 ], op, l );

            while( true )
            {
                op += ResampleFactor;
                l -= ResampleFactor;

                if( l <= 0 )
                {
                    break;
                }

                addArray( &fs.Flt[ 0 ], op, l );
            }
        }
        else
        if( !UseFltOrig )
        {
            fs.EdgePixelCount = fs.EdgePixelCountDef;
        }
    }

    /**
     * Function adds a correction filter that tries to achieve a linear
     * frequency response at all frequencies. The actual resulting response
     * may feature a slight damping of the highest frequencies since a
     * suitably short correction filter cannot fix steep high-frequency
     * damping.
     *
     * This function assumes that the resizing step is currently the last
     * step, even if it was not inserted yet: this allows placement of the
     * correction filter both before and after the resizing step.
     *
     * @param Steps Filtering steps.
     * @param bw Resulting bandwidth relative to the original bandwidth (which
     * is 1.0), usually 1/k. Should be <= 1.0.
     * @param IsPreCorrection "True" if the filtering step was already created
     * and it is first in the Steps array. "True" also adds edge pixels to
     * reduce edge artifacts.
     * @param IsModel "True" if filtering steps modeling is performed without
     * actual filter building.
     */

    void addCorrectionFilter( CFilterSteps& Steps, const double bw,
        const bool IsPreCorrection, const bool IsModel ) const
    {
        CFilterStep& fs = ( IsPreCorrection ? Steps[ 0 ] : Steps.add() );
        fs.IsUpsample = false;
        fs.ResampleFactor = 1;
        fs.DCGain = 1.0;
        fs.EdgePixelCount = ( IsPreCorrection ? fs.EdgePixelCountDef : 0 );

        if( IsModel )
        {
            allocFilter( fs.Flt, CDSPFIREQ :: calcFilterLength(
                Params.CorrFltLen, fs.FltLatency ), true );

            return;
        }

        const int BinCount = 65; // Frequency response bins to control.
        const int BinCount1 = BinCount - 1;
        double curbw = 1.0; // Bandwidth of the filter at the current step.
        int i;
        int j;
        double re;
        double im;

        CBuffer< double > Bins( BinCount ); // Adjustment introduced by all
            // steps at all frequencies of interest.

        for( j = 0; j < BinCount; j++ )
        {
            Bins[ j ] = 1.0;
        }

        const int si = ( IsPreCorrection ? 1 : 0 );

        for( i = si; i < Steps.getItemCount() - ( si ^ 1 ); i++ )
        {
            const CFilterStep& fs = Steps[ i ];

            if( fs.IsUpsample )
            {
                curbw *= fs.ResampleFactor;

                if( fs.FltOrig.getCapacity() > 0 )
                {
                    continue;
                }
            }

            const double dcg = 1.0 / fs.DCGain; // DC gain correction.
            const fptype* Flt;
            int FltLen;

            if( fs.ResampleFactor == 0 )
            {
                Flt = fs.FltBank -> getFilter( 0 );
                FltLen = fs.FltBank -> getFilterLen();
            }
            else
            {
                Flt = &fs.Flt[ 0 ];
                FltLen = fs.Flt.getCapacity();
            }

            // Calculate frequency response adjustment introduced by the
            // filter at this step, within the bounds of bandwidth of
            // interest.

            for( j = 0; j < BinCount; j++ )
            {
                const double th = AVIR_PI * bw / curbw * j / BinCount1;

                calcFIRFilterResponse( Flt, FltLen, th, re, im );

                Bins[ j ] /= sqrt( re * re + im * im ) * dcg;
            }

            if( !fs.IsUpsample && fs.ResampleFactor > 1 )
            {
                curbw /= fs.ResampleFactor;
            }
        }

        // Calculate filter.

        CDSPFIREQ EQ;
        EQ.init( bw * 2.0, Params.CorrFltLen, BinCount, 0.0, bw, false,
            Params.CorrFltAlpha );

        fs.FltLatency = EQ.getFilterLatency();

        CBuffer< double > Filter( EQ.getFilterLength() );
        EQ.buildFilter( Bins, &Filter[ 0 ]);
        normalizeFIRFilter( &Filter[ 0 ], Filter.getCapacity(), 1.0 );
        optimizeFIRFilter( Filter, fs.FltLatency );
        normalizeFIRFilter( &Filter[ 0 ], Filter.getCapacity(), 1.0 );

        allocFilter( fs.Flt, Filter.getCapacity() );
        copyArray( &Filter[ 0 ], &fs.Flt[ 0 ], Filter.getCapacity() );

        // Print a theoretically achieved final frequency response at various
        // feature sizes (from DC to 1 pixel). Values above 255 means features
        // become brighter, values below 255 means features become dimmer.

/*      const double sbw = ( bw > 1.0 ? 1.0 / bw : 1.0 );

        for( j = 0; j < BinCount; j++ )
        {
            const double th = AVIR_PI * sbw * j / BinCount1;

            calcFIRFilterResponse( &fs.Flt[ 0 ], fs.Flt.getCapacity(),
                th, re, im );

            printf( "%f\n", sqrt( re * re + im * im ) / Bins[ j ] * 255 );
        }

        printf( "***\n" );*/
    }

    /**
     * Function adds a sharpening filter if image is being upsized. Such
     * sharpening allows to spot interpolation filter's stop-band attenuation:
     * if attenuation is too weak, a "dark grid" and other artifacts may
     * become visible.
     *
     * It is assumed that 40 decibel stop-band attenuation should be
     * considered a required minimum: this allows application of (deliberately
     * strong) 64X sharpening without spotting any artifacts.
     *
     * @param Steps Filtering steps.
     * @param bw Resulting bandwidth relative to the original bandwidth (which
     * is 1.0), usually 1/k.
     * @param IsModel "True" if filtering steps modeling is performed without
     * actual filter building.
     */

    static void addSharpenTest( CFilterSteps& Steps, const double bw,
        const bool IsModel )
    {
        if( bw <= 1.0 )
        {
            return;
        }

        const double FltLen = 10.0 * bw;

        CFilterStep& fs = Steps.add();
        fs.IsUpsample = false;
        fs.ResampleFactor = 1;
        fs.DCGain = 1.0;
        fs.EdgePixelCount = 0;

        if( IsModel )
        {
            allocFilter( fs.Flt, CDSPFIREQ :: calcFilterLength( FltLen,
                fs.FltLatency ), true );

            return;
        }

        const int BinCount = 200;
        CBuffer< double > Bins( BinCount );
        int Thresh = (int) round( BinCount / bw * 1.75 );

        if( Thresh > BinCount )
        {
            Thresh = BinCount;
        }

        int j;

        for( j = 0; j < Thresh; j++ )
        {
            Bins[ j ] = 1.0;
        }

        for( j = Thresh; j < BinCount; j++ )
        {
            Bins[ j ] = 256.0;
        }

        CDSPFIREQ EQ;
        EQ.init( bw * 2.0, FltLen, BinCount, 0.0, bw, false, 1.7 );

        fs.FltLatency = EQ.getFilterLatency();

        CBuffer< double > Filter( EQ.getFilterLength() );
        EQ.buildFilter( Bins, &Filter[ 0 ]);
        normalizeFIRFilter( &Filter[ 0 ], Filter.getCapacity(), 1.0 );
        optimizeFIRFilter( Filter, fs.FltLatency );
        normalizeFIRFilter( &Filter[ 0 ], Filter.getCapacity(), 1.0 );

        allocFilter( fs.Flt, Filter.getCapacity() );
        copyArray( &Filter[ 0 ], &fs.Flt[ 0 ], Filter.getCapacity() );

/*      for( j = 0; j < BinCount; j++ )
        {
            const double th = AVIR_PI * j / ( BinCount - 1 );
            double re;
            double im;

            calcFIRFilterResponse( &fs.Flt[ 0 ], fs.Flt.getCapacity(),
                th, re, im );

            printf( "%f\n", sqrt( re * re + im * im ));
        }

        printf( "***\n" );*/
    }

    /**
     * Function builds sequence of filtering steps depending on the specified
     * resizing coefficient. The last steps included are always the resizing
     * step then (possibly) the correction step.
     *
     * @param Steps Array that receives filtering steps.
     * @param[out] Vars Variables object.
     * @param FltBank Filter bank to initialize and use.
     * @param DCGain The overall DC gain to apply. This DC gain is applied to
     * the first filtering step only (upsampling or filtering step).
     * @param ModeFlags Build mode flags to use. This is a bitmap of switches
     * that enable or disable certain algorithm features.
     * @param IsModel "True" if filtering steps modeling is performed without
     * the actual filter allocation and building.
     */

    void buildFilterSteps( CFilterSteps& Steps, CImageResizerVars& Vars,
        CDSPFracFilterBankLin< fptype >& FltBank, const double DCGain,
        const int ModeFlags, const bool IsModel ) const
    {
        Steps.clear();

        const bool DoFltAndIntCombo = (( ModeFlags & 1 ) != 0 ); // Do filter
            // and interpolator combining.
        const bool ForceHiOrderInt = (( ModeFlags & 2 ) != 0 ); // Force use
            // of a higher-order interpolation.
        const bool UseHalfband = (( ModeFlags & 4 ) != 0 ); // Use half-band
            // filter.

        const double bw = 1.0 / Vars.k; // Resulting bandwidth.
        const int UpsampleFactor = ( (int) floor( Vars.k ) < 2 ? 2 : 1 );
        double IntCutoffMult; // Interpolation filter cutoff multiplier.
        CFilterStep* ReuseStep; // If not NULL, resizing step should use
            // this step object instead of creating a new one.
        CFilterStep* ExtFltStep; // Use FltOrig of this step as the external
            // filter to applied to the interpolator.
        bool IsPreCorrection; // "True" if the correction filter is applied
            // first.
        double FltCutoff; // Cutoff frequency of the first filtering step.
        double corrbw; ///< Bandwidth at the correction step.

        if( Vars.k <= 1.0 )
        {
            IsPreCorrection = true;
            FltCutoff = 1.0;
            corrbw = 1.0;
            Steps.add();
        }
        else
        {
            IsPreCorrection = false;
            FltCutoff = bw;
            corrbw = bw;
        }

        // Add 1 upsampling or several downsampling filters.

        if( UpsampleFactor > 1 )
        {
            CFilterStep& fs = Steps.add();
            assignFilterParams( fs, true, UpsampleFactor, FltCutoff, DCGain,
                DoFltAndIntCombo, IsModel );

            IntCutoffMult = FltCutoff * 2.0 / UpsampleFactor;
            ReuseStep = nullptr;
            ExtFltStep = ( DoFltAndIntCombo ? &fs : nullptr );
        }
        else
        {
            int DownsampleFactor;

            while( true )
            {
                DownsampleFactor = (int) floor( 0.5 / FltCutoff );
                bool DoHBFltAdd;

                if( DownsampleFactor > 16 )
                {
                    // Add half-band filter unconditionally in order to keep
                    // filter lengths lower for more precise frequency
                    // response and less edge artifacts.

                    DoHBFltAdd = true;
                    DownsampleFactor = 16;
                }
                else
                {
                    DoHBFltAdd = ( UseHalfband && DownsampleFactor > 1 );
                }

                if( DoHBFltAdd )
                {
                    assignFilterParams( Steps.add(), false, DownsampleFactor,
                        0.0, 1.0, false, IsModel );

                    FltCutoff *= DownsampleFactor;
                }
                else
                {
                    if( DownsampleFactor < 1 )
                    {
                        DownsampleFactor = 1;
                    }

                    break;
                }
            }

            CFilterStep& fs = Steps.add();
            assignFilterParams( fs, false, DownsampleFactor, FltCutoff,
                DCGain, DoFltAndIntCombo, IsModel );

            IntCutoffMult = FltCutoff / 0.5;

            if( DoFltAndIntCombo )
            {
                ReuseStep = &fs;
                ExtFltStep = &fs;
            }
            else
            {
                IntCutoffMult *= DownsampleFactor;
                ReuseStep = nullptr;
                ExtFltStep = nullptr;
            }
        }

        // Insert resizing and correction steps.

        CFilterStep& fs = ( ReuseStep == nullptr ? Steps.add() : *ReuseStep );

        Vars.ResizeStep = Steps.getItemCount() - 1;
        fs.IsUpsample = false;
        fs.ResampleFactor = 0;
        fs.DCGain = ( ExtFltStep == nullptr ? 1.0 : ExtFltStep -> DCGain );

        initFilterBank( FltBank, IntCutoffMult, ForceHiOrderInt,
            ( ExtFltStep == nullptr ? fs.FltOrig : ExtFltStep -> FltOrig ));

        if( FltBank == FixedFilterBank )
        {
            fs.FltBank = (CDSPFracFilterBankLin< fptype >*) &FixedFilterBank;
        }
        else
        {
            fs.FltBank = &FltBank;
        }

        addCorrectionFilter( Steps, corrbw, IsPreCorrection, IsModel );

        //addSharpenTest( Steps, bw, IsModel );
    }

    /**
     * Function extends *this upsampling step so that it produces more
     * upsampled pixels that cover the prefix and suffix needs of the next
     * step. After the call to this function the InPrefix and InSuffix
     * variables of the next step will be set to zero.
     *
     * @param fs Upsampling filtering step.
     * @param NextStep The next step structure.
     */

    static void extendUpsample( CFilterStep& fs, CFilterStep& NextStep )
    {
        fs.InPrefix = ( NextStep.InPrefix + fs.ResampleFactor - 1 ) /
            fs.ResampleFactor;

        fs.OutPrefix += fs.InPrefix * fs.ResampleFactor;
        NextStep.InPrefix = 0;

        fs.InSuffix = ( NextStep.InSuffix + fs.ResampleFactor - 1 ) /
            fs.ResampleFactor;

        fs.OutSuffix += fs.InSuffix * fs.ResampleFactor;
        NextStep.InSuffix = 0;
    }

    /**
     * Function fills resizing step's RPosBuf array, excluding the actual
     * "ftp" pointers and "SrcOffs" offsets.
     *
     * This array should be cleared if the resizing step or offset were
     * changed. Otherwise this function only fills the elements required to
     * cover resizing step's OutLen.
     *
     * This function is called by the updateFilterStepBuffers() function.
     *
     * @param fs Resizing step.
     * @param Vars Variables object.
     */

    static void fillRPosBuf( CFilterStep& fs, const CImageResizerVars& Vars )
    {
        const int PrevLen = fs.RPosBuf -> getCapacity();

        if( fs.OutLen > PrevLen )
        {
            fs.RPosBuf -> increaseCapacity( fs.OutLen );
        }

        typename CFilterStep :: CResizePos* rpos = &(*fs.RPosBuf)[ PrevLen ];
        const int FracCount = fs.FltBank -> getFracCount();
        const double o = Vars.o;
        const double k = Vars.k;
        int i;

        for( i = PrevLen; i < fs.OutLen; i++ )
        {
            const double SrcPos = o + k * i;
            const int SrcPosInt = (int) floor( SrcPos );
            const double x = ( SrcPos - SrcPosInt ) * FracCount;
            const int fti = (int) x;
            rpos -> x = (typename fpclass :: fptypeatom) ( x - fti );
            rpos -> fti = fti;
            rpos -> SrcPosInt = SrcPosInt;
            rpos++;
        }
    }

    /**
     * Function updates filtering step buffer lengths depending on the
     * specified source and new scanline lengths. This function should be
     * called after the buildFilterSteps() function.
     *
     * @param Steps Array that receives filtering steps.
     * @param[out] Vars Variables object, will receive buffer size and length.
     * This function expects "k" and "o" variable values that will be
     * adjusted by this function.
     * @param RPosBufArray Resizing position buffers array, used to obtain
     * buffer to initialize and use (will be reused if it is already fully or
     * partially filled).
     * @param SrcLen Source scanline's length in pixels.
     * @param NewLen New scanline's length in pixels.
     */

    static void updateFilterStepBuffers( CFilterSteps& Steps,
        CImageResizerVars& Vars,
        typename CFilterStep :: CRPosBufArray& RPosBufArray, int SrcLen,
        const int NewLen )
    {
        int upstep = -1;
        int InBuf = 0;
        int i;

        for( i = 0; i < Steps.getItemCount(); i++ )
        {
            CFilterStep& fs = Steps[ i ];

            fs.Vars = &Vars;
            fs.InLen = SrcLen;
            fs.InBuf = InBuf;
            fs.OutBuf = ( InBuf + 1 ) & 1;

            if( fs.IsUpsample )
            {
                upstep = i;
                Vars.k *= fs.ResampleFactor;
                Vars.o *= fs.ResampleFactor;
                fs.InPrefix = 0;
                fs.InSuffix = 0;
                fs.OutLen = fs.InLen * fs.ResampleFactor;
                fs.OutPrefix = fs.FltLatency;
                fs.OutSuffix = fs.Flt.getCapacity() - fs.FltLatency -
                    fs.ResampleFactor;

                int l0 = fs.OutPrefix + fs.OutLen + fs.OutSuffix;
                int l = fs.InLen * fs.ResampleFactor +
                    fs.SuffixDC.getCapacity();

                if( l > l0 )
                {
                    fs.OutSuffix += l - l0;
                }

                l0 = fs.OutLen + fs.OutSuffix;

                if( fs.PrefixDC.getCapacity() > l0 )
                {
                    fs.OutSuffix += fs.PrefixDC.getCapacity() - l0;
                }
            }
            else
            if( fs.ResampleFactor == 0 )
            {
                const int FilterLenD2 = fs.FltBank -> getFilterLen() / 2;
                const int FilterLenD21 = FilterLenD2 - 1;

                const int ResizeLPix = (int) floor( Vars.o ) - FilterLenD21;
                fs.InPrefix = ( ResizeLPix < 0 ? -ResizeLPix : 0 );
                const int ResizeRPix = (int) floor( Vars.o +
                    ( NewLen - 1 ) * Vars.k ) + FilterLenD2 + 1;

                fs.InSuffix = ( ResizeRPix > fs.InLen ?
                    ResizeRPix - fs.InLen : 0 );

                fs.OutLen = NewLen;
                fs.RPosBuf = &RPosBufArray.getRPosBuf( Vars.k, Vars.o,
                    fs.FltBank -> getFracCount() );

                fillRPosBuf( fs, Vars );
            }
            else
            {
                Vars.k /= fs.ResampleFactor;
                Vars.o /= fs.ResampleFactor;
                Vars.o += fs.EdgePixelCount;

                fs.InPrefix = fs.FltLatency;
                fs.InSuffix = fs.Flt.getCapacity() - fs.FltLatency - 1;

                // Additionally extend OutLen to produce more precise edge
                // pixels.

                fs.OutLen = ( fs.InLen + fs.ResampleFactor - 1 ) /
                    fs.ResampleFactor + fs.EdgePixelCount;

                fs.InSuffix += ( fs.OutLen - 1 ) * fs.ResampleFactor + 1 -
                    fs.InLen;

                fs.InPrefix += fs.EdgePixelCount * fs.ResampleFactor;
                fs.OutLen += fs.EdgePixelCount;
            }

            InBuf = fs.OutBuf;
            SrcLen = fs.OutLen;
        }

        Steps[ Steps.getItemCount() - 1 ].OutBuf = 2;

        if( upstep != -1 )
        {
            extendUpsample( Steps[ upstep ], Steps[ upstep + 1 ]);
        }
    }

    /**
     * Function calculates an optimal intermediate buffer length that will
     * cover all needs of the specified filtering steps. This function should
     * be called after the updateFilterStepBuffers() function.
     *
     * Function also updates resizing step's RPosBuf pointers to the filter
     * bank and SrcOffs values.
     *
     * @param Steps Filtering steps.
     * @param[out] Vars Variables object, will receive buffer size and length.
     * @param ResElIncr Resulting (final) element increment, used to produce
     * de-interleaved result. For horizontal processing this value is equal
     * to last step's OutLen, for vertical processing this value is equal to
     * resulting image's width.
     */

    static void updateBufLenAndRPosPtrs( CFilterSteps& Steps,
        CImageResizerVars& Vars, const int ResElIncr )
    {
        int MaxPrefix[ 2 ] = { 0, 0 };
        int MaxLen[ 2 ] = { 0, 0 };
        int i;

        for( i = 0; i < Steps.getItemCount(); i++ )
        {
            CFilterStep& fs = Steps[ i ];
            const int ib = fs.InBuf;

            if( fs.InPrefix > MaxPrefix[ ib ])
            {
                MaxPrefix[ ib ] = fs.InPrefix;
            }

            int l = fs.InLen + fs.InSuffix;

            if( l > MaxLen[ ib ])
            {
                MaxLen[ ib ] = l;
            }

            fs.InElIncr = fs.InPrefix + l;

            if( fs.OutBuf == 2 )
            {
                break;
            }

            const int ob = fs.OutBuf;

            if( fs.IsUpsample )
            {
                if( fs.OutPrefix > MaxPrefix[ ob ])
                {
                    MaxPrefix[ ob ] = fs.OutPrefix;
                }

                l = fs.OutLen + fs.OutSuffix;

                if( l > MaxLen[ ob ])
                {
                    MaxLen[ ob ] = l;
                }
            }
            else
            {
                if( fs.OutLen > MaxLen[ ob ])
                {
                    MaxLen[ ob ] = fs.OutLen;
                }
            }
        }

        // Update OutElIncr values of all steps.

        for( i = 0; i < Steps.getItemCount(); i++ )
        {
            CFilterStep& fs = Steps[ i ];

            if( fs.OutBuf == 2 )
            {
                fs.OutElIncr = ResElIncr;
                break;
            }

            CFilterStep& fs2 = Steps[ i + 1 ];

            if( fs.IsUpsample )
            {
                fs.OutElIncr = fs.OutPrefix + fs.OutLen + fs.OutSuffix;

                if( fs.OutElIncr > fs2.InElIncr )
                {
                    fs2.InElIncr = fs.OutElIncr;
                }
                else
                {
                    fs.OutElIncr = fs2.InElIncr;
                }
            }
            else
            {
                fs.OutElIncr = fs2.InElIncr;
            }
        }

        // Update temporary buffer's length.

        for( i = 0; i < 2; i++ )
        {
            Vars.BufLen[ i ] = MaxPrefix[ i ] + MaxLen[ i ];
            Vars.BufOffs[ i ] = MaxPrefix[ i ];

            if( Vars.packmode == 0 )
            {
                Vars.BufOffs[ i ] *= Vars.ElCount;
            }

            Vars.BufLen[ i ] *= Vars.ElCount;
        }

        // Update RPosBuf pointers and SrcOffs.

        CFilterStep& fs = Steps[ Vars.ResizeStep ];
        typename CFilterStep :: CResizePos* rpos = &(*fs.RPosBuf)[ 0 ];
        const int em = ( fpclass :: packmode == 0 ? Vars.ElCount : 1 );
        const int FilterLenD21 = fs.FltBank -> getFilterLen() / 2 - 1;

        for( i = 0; i < fs.OutLen; i++ )
        {
            rpos -> ftp = fs.FltBank -> getFilter( rpos -> fti );
            rpos -> SrcOffs = ( rpos -> SrcPosInt - FilterLenD21 ) * em;
            rpos++;
        }
    }

    /**
     * Function modifies the overall (DC) gain of the correction filter in the
     * pre-built filtering steps array.
     *
     * @param Steps Filtering steps.
     * @param m Multiplier to apply to the correction filter.
     */

    void modifyCorrFilterDCGain( CFilterSteps& Steps, const double m ) const
    {
        CBuffer< fptype >* Flt;
        const int z = Steps.getItemCount() - 1;

        if( !Steps[ z ].IsUpsample && Steps[ z ].ResampleFactor == 1 )
        {
            Flt = &Steps[ z ].Flt;
        }
        else
        {
            Flt = &Steps[ 0 ].Flt;
        }

        int i;

        for( i = 0; i < Flt -> getCapacity(); i++ )
        {
            (*Flt)[ i ] = (fptype) ( (double) (*Flt)[ i ] * m );
        }
    }

    /**
     * Function builds a map of used fractional delay filters based on the
     * resizing positions buffer.
     *
     * @param fs Resizing step.
     * @param[out] UsedFracMap Map of used fractional delay filters.
     */

    static void fillUsedFracMap( const CFilterStep& fs,
        CBuffer< uint8_t >& UsedFracMap )
    {
        const int FracCount = fs.FltBank -> getFracCount();
        UsedFracMap.increaseCapacity( FracCount, false );
        memset( &UsedFracMap[ 0 ], 0, FracCount * sizeof( UsedFracMap[ 0 ]));

        typename CFilterStep :: CResizePos* rpos = &(*fs.RPosBuf)[ 0 ];
        int i;

        for( i = 0; i < fs.OutLen; i++ )
        {
            UsedFracMap[ rpos -> fti ] |= 1;
            rpos++;
        }
    }

    /**
     * Function calculates the overall filtering steps complexity per
     * scanline. Each complexity unit corresponds to a single multiply-add
     * operation. Data copy and pointer math operations are not included in
     * this calculation, it is assumed that they correlate to the multiply-add
     * operations. Calculation also does not include final rounding, dithering
     * and clamping operations since they cannot be optimized out anyway.
     *
     * Calculation of the CRPosBuf buffer is not included since it cannot be
     * avoided.
     *
     * This function should be called after the updateFilterStepBuffers()
     * function.
     *
     * @param Steps Filtering steps array.
     * @param Vars Variables object.
     * @param UsedFracMap The map of used fractional delay filters.
     * @param ScanlineCount Scanline count.
     */

    static int calcComplexity( const CFilterSteps& Steps,
        const CImageResizerVars& Vars, const CBuffer< uint8_t >& UsedFracMap,
        const int ScanlineCount )
    {
        int fcnum; // Filter complexity multiplier numerator.
        int fcdenom; // Filter complexity multiplier denominator.

        if( Vars.packmode != 0 )
        {
            fcnum = 1;
            fcdenom = 1;
        }
        else
        {
            // In interleaved processing mode, filters require 1 less
            // multiplication per 2 multiply-add instructions.

            fcnum = 3;
            fcdenom = 4;
        }

        int s = 0; // Complexity per one scanline.
        int s2 = 0; // Complexity per all scanlines.
        int i;

        for( i = 0; i < Steps.getItemCount(); i++ )
        {
            const CFilterStep& fs = Steps[ i ];

            s2 += 65 * fs.Flt.getCapacity(); // Filter creation complexity.

            if( fs.IsUpsample )
            {
                if( fs.FltOrig.getCapacity() > 0 )
                {
                    continue;
                }

                s += ( fs.Flt.getCapacity() *
                    ( fs.InPrefix + fs.InLen + fs.InSuffix ) +
                    fs.SuffixDC.getCapacity() + fs.PrefixDC.getCapacity() ) *
                    Vars.ElCount;
            }
            else
            if( fs.ResampleFactor == 0 )
            {
                s += fs.FltBank -> getFilterLen() *
                    ( fs.FltBank -> getOrder() + Vars.ElCount ) * fs.OutLen;

                s2 += fs.FltBank -> calcInitComplexity( UsedFracMap );
            }
            else
            {
                s += fs.Flt.getCapacity() * Vars.ElCount * fs.OutLen *
                    fcnum / fcdenom;
            }
        }

        return( s + s2 / ScanlineCount );
    }

    /**
     * @brief Thread-isolated data used for scanline processing.
     *
     * This structure holds data necessary for image's horizontal or vertical
     * scanline processing, including scanline processing queue.
     *
     * @tparam Tin Source element data type. Intermediate buffers store data
     * in floating point format.
     * @tparam Tout Destination element data type. Intermediate buffers store
     * data in floating point format.
     */

    template< class Tin, class Tout >
    class CThreadData : public CImageResizerThreadPool :: CWorkload
    {
    public:
        virtual void process()
        {
            processScanlineQueue();
        }

        /**
         * This enumeration lists possible scanline operations.
         */

        enum EScanlineOperation
        {
            sopResizeH, ///< Resize horizontal scanline.
                ///<
            sopResizeV, ///< Resize vertical scanline.
                ///<
            sopDitherAndUnpackH, ///< Dither and unpack horizontal scanline.
                ///<
            sopUnpackH ///< Unpack horizontal scanline.
                ///<
        };

        /**
         * Function initializes *this thread data object and assigns certain
         * variables provided by the higher level code.
         *
         * @param aThreadIndex Index of this thread data (0-based).
         * @param aThreadCount Total number of threads used during processing.
         * @param aSteps Filtering steps.
         * @param aVars Image resizer variables.
         */

        void init( const int aThreadIndex, const int aThreadCount,
            const CFilterSteps& aSteps, const CImageResizerVars& aVars )
        {
            ThreadIndex = aThreadIndex;
            ThreadCount = aThreadCount;
            Steps = &aSteps;
            Vars = &aVars;
        }

        /**
         * Function initializes scanline processing queue, and updates
         * capacities of intermediate buffers.
         *
         * @param aOp Operation to perform over scanline.
         * @param TotalLines The total number of scanlines that will be
         * processed by all threads.
         * @param aSrcLen Source scanline length in pixels.
         * @param aSrcIncr Source scanline buffer increment. Ignored in
         * horizontal scanline processing.
         * @param aResIncr Resulting scanline buffer increment. Ignored in
         * horizontal scanline processing.
         */

        void initScanlineQueue( const EScanlineOperation aOp,
            const int TotalLines, const int aSrcLen, const int aSrcIncr = 0,
            const int aResIncr = 0 )
        {
            const int l = Vars -> BufLen[ 0 ] + Vars -> BufLen[ 1 ];

            if( Bufs.getCapacity() < l )
            {
                Bufs.alloc( l, fpclass :: fpalign );
            }

            BufPtrs[ 0 ] = Bufs + Vars -> BufOffs[ 0 ];
            BufPtrs[ 1 ] = Bufs + Vars -> BufLen[ 0 ] + Vars -> BufOffs[ 1 ];

            int j;
            int ml = 0;

            for( j = 0; j < Steps -> getItemCount(); j++ )
            {
                const CFilterStep& fs = (*Steps)[ j ];

                if( fs.ResampleFactor == 0 &&
                    ml < fs.FltBank -> getFilterLen() )
                {
                    ml = fs.FltBank -> getFilterLen();
                }
            }

            TmpFltBuf.alloc( ml, fpclass :: fpalign );
            ScanlineOp = aOp;
            SrcLen = aSrcLen;
            SrcIncr = aSrcIncr;
            ResIncr = aResIncr;
            QueueLen = 0;
            Queue.increaseCapacity(( TotalLines + ThreadCount - 1 ) /
                ThreadCount, false );
        }

        /**
         * Function adds a scanline to the queue buffer. The
         * initScanlineQueue() function should be called before calling this
         * function. The number of calls to this add function should not
         * exceed the TotalLines spread over all threads.
         *
         * @param SrcBuf Source scanline buffer.
         * @param ResBuf Resulting scanline buffer.
         */

        void addScanlineToQueue( void* const SrcBuf, void* const ResBuf )
        {
            Queue[ QueueLen ].SrcBuf = SrcBuf;
            Queue[ QueueLen ].ResBuf = ResBuf;
            QueueLen++;
        }

        /**
         * Function processes all queued scanlines.
         */

        void processScanlineQueue()
        {
            int i;

            switch( ScanlineOp )
            {
                case sopResizeH:
                {
                    for( i = 0; i < QueueLen; i++ )
                    {
                        resizeScanlineH( (Tin*) Queue[ i ].SrcBuf,
                            (fptype*) Queue[ i ].ResBuf );
                    }

                    break;
                }

                case sopResizeV:
                {
                    for( i = 0; i < QueueLen; i++ )
                    {
                        resizeScanlineV( (fptype*) Queue[ i ].SrcBuf,
                            (fptype*) Queue[ i ].ResBuf );
                    }

                    break;
                }

                case sopDitherAndUnpackH:
                {
                    if( Vars -> UseSRGBGamma )
                    {
                        for( i = 0; i < QueueLen; i++ )
                        {
                            CFilterStep :: applySRGBGamma(
                                (fptype*) Queue[ i ].SrcBuf, SrcLen, *Vars );

                            Ditherer.dither( (fptype*) Queue[ i ].SrcBuf );

                            CFilterStep :: unpackScanline(
                                (fptype*) Queue[ i ].SrcBuf,
                                (Tout*) Queue[ i ].ResBuf, SrcLen, *Vars );
                        }
                    }
                    else
                    {
                        for( i = 0; i < QueueLen; i++ )
                        {
                            Ditherer.dither( (fptype*) Queue[ i ].SrcBuf );

                            CFilterStep :: unpackScanline(
                                (fptype*) Queue[ i ].SrcBuf,
                                (Tout*) Queue[ i ].ResBuf, SrcLen, *Vars );
                        }
                    }

                    break;
                }

                case sopUnpackH:
                {
                    if( Vars -> UseSRGBGamma )
                    {
                        for( i = 0; i < QueueLen; i++ )
                        {
                            CFilterStep :: applySRGBGamma(
                                (fptype*) Queue[ i ].SrcBuf, SrcLen, *Vars );

                            CFilterStep :: unpackScanline(
                                (fptype*) Queue[ i ].SrcBuf,
                                (Tout*) Queue[ i ].ResBuf, SrcLen, *Vars );
                        }
                    }
                    else
                    {
                        for( i = 0; i < QueueLen; i++ )
                        {
                            CFilterStep :: unpackScanline(
                                (fptype*) Queue[ i ].SrcBuf,
                                (Tout*) Queue[ i ].ResBuf, SrcLen, *Vars );
                        }
                    }

                    break;
                }
            }
        }

        /**
         * Function returns ditherer object associated with *this thread data
         * object.
         */

        CDitherer& getDitherer()
        {
            return( Ditherer );
        }

    private:
        int ThreadIndex; ///< Thread index.
            ///<
        int ThreadCount; ///< Thread count.
            ///<
        const CFilterSteps* Steps; ///< Filtering steps.
            ///<
        const CImageResizerVars* Vars; ///< Image resizer variables.
            ///<
        CBuffer< fptype > Bufs; ///< Flip-flop intermediate buffers.
            ///<
        fptype* BufPtrs[ 3 ]; ///< Flip-flop buffer pointers (referenced by
            ///< filtering step's InBuf and OutBuf indices).
            ///<
        CBuffer< fptype > TmpFltBuf; ///< Temporary buffer used in the
            ///< doResize() function, aligned by fpclass :: fpalign.
            ///<
        EScanlineOperation ScanlineOp; ///< Operation to perform over
            ///< scanline.
            ///<
        int SrcLen; ///< Source scanline length in the last queue.
            ///<
        int SrcIncr; ///< Source scanline buffer increment in the last queue.
            ///<
        int ResIncr; ///< Resulting scanline buffer increment in the last
            ///< queue.
            ///<
        CDitherer Ditherer; ///< Ditherer object to use.
            ///<

        /**
         * @brief Scanline processing queue item.
         *
         * Scanline processing queue item.
         */

        struct CQueueItem
        {
            void* SrcBuf; ///< Source scanline buffer, will by typecasted to
                ///< Tin or fptype*.
                ///<
            void* ResBuf; ///< Resulting scanline buffer, will by typecasted
                ///< to Tout or fptype*.
                ///<
        };

        CBuffer< CQueueItem > Queue; ///< Scanline processing queue.
            ///<
        int QueueLen; ///< Queue length.
            ///<

        /**
         * Function resizes a single horizontal scanline.
         *
         * @param SrcBuf Source scanline buffer. Can be either horizontal or
         * vertical.
         * @param ResBuf Resulting scanline buffer.
         */

        void resizeScanlineH( const Tin* const SrcBuf, fptype* const ResBuf )
        {
            (*Steps)[ 0 ].packScanline( SrcBuf, BufPtrs[ 0 ], SrcLen );
            BufPtrs[ 2 ] = ResBuf;
            int j;

            for( j = 0; j < Steps -> getItemCount(); j++ )
            {
                const CFilterStep& fs = (*Steps)[ j ];
                fs.prepareInBuf( BufPtrs[ fs.InBuf ]);
                const int DstIncr =
                    ( Vars -> packmode == 0 ? Vars -> ElCount : 1 );

                if( fs.ResampleFactor != 0 )
                {
                    if( fs.IsUpsample )
                    {
                        fs.doUpsample( BufPtrs[ fs.InBuf ],
                            BufPtrs[ fs.OutBuf ]);
                    }
                    else
                    {
                        fs.doFilter( BufPtrs[ fs.InBuf ],
                            BufPtrs[ fs.OutBuf ], DstIncr );
                    }
                }
                else
                {
                    fs.doResize( BufPtrs[ fs.InBuf ], BufPtrs[ fs.OutBuf ],
                        DstIncr, TmpFltBuf );
                }
            }
        }

        /**
         * Function resizes a single vertical scanline.
         *
         * @param SrcBuf Source scanline buffer. Can be either horizontal or
         * vertical.
         * @param ResBuf Resulting scanline buffer.
         */

        void resizeScanlineV( const fptype* const SrcBuf,
            fptype* const ResBuf )
        {
            (*Steps)[ 0 ].convertVtoH( SrcBuf, BufPtrs[ 0 ], SrcLen,
                SrcIncr );

            BufPtrs[ 2 ] = ResBuf;
            int j;

            for( j = 0; j < Steps -> getItemCount(); j++ )
            {
                const CFilterStep& fs = (*Steps)[ j ];
                fs.prepareInBuf( BufPtrs[ fs.InBuf ]);
                const int DstIncr = ( fs.OutBuf == 2 ? ResIncr :
                    ( Vars -> packmode == 0 ? Vars -> ElCount : 1 ));

                if( fs.ResampleFactor != 0 )
                {
                    if( fs.IsUpsample )
                    {
                        fs.doUpsample( BufPtrs[ fs.InBuf ],
                            BufPtrs[ fs.OutBuf ]);
                    }
                    else
                    {
                        fs.doFilter( BufPtrs[ fs.InBuf ],
                            BufPtrs[ fs.OutBuf ], DstIncr );
                    }
                }
                else
                {
                    fs.doResize( BufPtrs[ fs.InBuf ], BufPtrs[ fs.OutBuf ],
                        DstIncr, TmpFltBuf );
                }
            }
        }
    };
};

#undef AVIR_PI
#undef AVIR_PId2

} // namespace avir

#endif // AVIR_CIMAGERESIZER_INCLUDED