ffmpeg/libswscale/swscale.c

/*
 * Copyright (C) 2001-2011 Michael Niedermayer <michaelni@gmx.at>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <inttypes.h>
#include <string.h>
#include <math.h>
#include <stdio.h>
#include "config.h"
#include <assert.h>
#include "swscale.h"
#include "swscale_internal.h"
#include "rgb2rgb.h"
#include "libavutil/avassert.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/cpu.h"
#include "libavutil/avutil.h"
#include "libavutil/mathematics.h"
#include "libavutil/bswap.h"
#include "libavutil/pixdesc.h"

DECLARE_ALIGNED(8, const uint8_t, dither_8x8_128)[8][8] = {
{  36, 68, 60, 92, 34, 66, 58, 90,},
{ 100,  4,124, 28, 98,  2,122, 26,},
{  52, 84, 44, 76, 50, 82, 42, 74,},
{ 116, 20,108, 12,114, 18,106, 10,},
{  32, 64, 56, 88, 38, 70, 62, 94,},
{  96,  0,120, 24,102,  6,126, 30,},
{  48, 80, 40, 72, 54, 86, 46, 78,},
{ 112, 16,104,  8,118, 22,110, 14,},
};
DECLARE_ALIGNED(8, const uint8_t, ff_sws_pb_64)[8] =
{  64, 64, 64, 64, 64, 64, 64, 64 };


static av_always_inline void fillPlane(uint8_t* plane, int stride,
                                       int width, int height,
                                       int y, uint8_t val)
{
    int i;
    uint8_t *ptr = plane + stride*y;
    for (i=0; i<height; i++) {
        memset(ptr, val, width);
        ptr += stride;
    }
}

static void hScale16To19_c(SwsContext *c, int16_t *_dst, int dstW, const uint8_t *_src,
                           const int16_t *filter,
                           const int32_t *filterPos, int filterSize)
{
    int i;
    int32_t *dst = (int32_t *) _dst;
    const uint16_t *src = (const uint16_t *) _src;
    int bits = av_pix_fmt_descriptors[c->srcFormat].comp[0].depth_minus1;
    int sh = bits - 4;

    if((isAnyRGB(c->srcFormat) || c->srcFormat==PIX_FMT_PAL8) && av_pix_fmt_descriptors[c->srcFormat].comp[0].depth_minus1<15)
        sh= 9;

    for (i = 0; i < dstW; i++) {
        int j;
        int srcPos = filterPos[i];
        int val = 0;

        for (j = 0; j < filterSize; j++) {
            val += src[srcPos + j] * filter[filterSize * i + j];
        }
        // filter=14 bit, input=16 bit, output=30 bit, >> 11 makes 19 bit
        dst[i] = FFMIN(val >> sh, (1 << 19) - 1);
    }
}

static void hScale16To15_c(SwsContext *c, int16_t *dst, int dstW, const uint8_t *_src,
                           const int16_t *filter,
                           const int32_t *filterPos, int filterSize)
{
    int i;
    const uint16_t *src = (const uint16_t *) _src;
    int sh = av_pix_fmt_descriptors[c->srcFormat].comp[0].depth_minus1;

    if(sh<15)
        sh= isAnyRGB(c->srcFormat) || c->srcFormat==PIX_FMT_PAL8 ? 13 : av_pix_fmt_descriptors[c->srcFormat].comp[0].depth_minus1;

    for (i = 0; i < dstW; i++) {
        int j;
        int srcPos = filterPos[i];
        int val = 0;

        for (j = 0; j < filterSize; j++) {
            val += src[srcPos + j] * filter[filterSize * i + j];
        }
        // filter=14 bit, input=16 bit, output=30 bit, >> 15 makes 15 bit
        dst[i] = FFMIN(val >> sh, (1 << 15) - 1);
    }
}

// bilinear / bicubic scaling
static void hScale8To15_c(SwsContext *c, int16_t *dst, int dstW, const uint8_t *src,
                          const int16_t *filter, const int32_t *filterPos,
                          int filterSize)
{
    int i;
    for (i=0; i<dstW; i++) {
        int j;
        int srcPos= filterPos[i];
        int val=0;
        for (j=0; j<filterSize; j++) {
            val += ((int)src[srcPos + j])*filter[filterSize*i + j];
        }
        //filter += hFilterSize;
        dst[i] = FFMIN(val>>7, (1<<15)-1); // the cubic equation does overflow ...
        //dst[i] = val>>7;
    }
}

static void hScale8To19_c(SwsContext *c, int16_t *_dst, int dstW, const uint8_t *src,
                          const int16_t *filter, const int32_t *filterPos,
                          int filterSize)
{
    int i;
    int32_t *dst = (int32_t *) _dst;
    for (i=0; i<dstW; i++) {
        int j;
        int srcPos= filterPos[i];
        int val=0;
        for (j=0; j<filterSize; j++) {
            val += ((int)src[srcPos + j])*filter[filterSize*i + j];
        }
        //filter += hFilterSize;
        dst[i] = FFMIN(val>>3, (1<<19)-1); // the cubic equation does overflow ...
        //dst[i] = val>>7;
    }
}

//FIXME all pal and rgb srcFormats could do this convertion as well
//FIXME all scalers more complex than bilinear could do half of this transform
static void chrRangeToJpeg_c(int16_t *dstU, int16_t *dstV, int width)
{
    int i;
    for (i = 0; i < width; i++) {
        dstU[i] = (FFMIN(dstU[i],30775)*4663 - 9289992)>>12; //-264
        dstV[i] = (FFMIN(dstV[i],30775)*4663 - 9289992)>>12; //-264
    }
}
static void chrRangeFromJpeg_c(int16_t *dstU, int16_t *dstV, int width)
{
    int i;
    for (i = 0; i < width; i++) {
        dstU[i] = (dstU[i]*1799 + 4081085)>>11; //1469
        dstV[i] = (dstV[i]*1799 + 4081085)>>11; //1469
    }
}
static void lumRangeToJpeg_c(int16_t *dst, int width)
{
    int i;
    for (i = 0; i < width; i++)
        dst[i] = (FFMIN(dst[i],30189)*19077 - 39057361)>>14;
}
static void lumRangeFromJpeg_c(int16_t *dst, int width)
{
    int i;
    for (i = 0; i < width; i++)
        dst[i] = (dst[i]*14071 + 33561947)>>14;
}

static void chrRangeToJpeg16_c(int16_t *_dstU, int16_t *_dstV, int width)
{
    int i;
    int32_t *dstU = (int32_t *) _dstU;
    int32_t *dstV = (int32_t *) _dstV;
    for (i = 0; i < width; i++) {
        dstU[i] = (FFMIN(dstU[i],30775<<4)*4663 - (9289992<<4))>>12; //-264
        dstV[i] = (FFMIN(dstV[i],30775<<4)*4663 - (9289992<<4))>>12; //-264
    }
}
static void chrRangeFromJpeg16_c(int16_t *_dstU, int16_t *_dstV, int width)
{
    int i;
    int32_t *dstU = (int32_t *) _dstU;
    int32_t *dstV = (int32_t *) _dstV;
    for (i = 0; i < width; i++) {
        dstU[i] = (dstU[i]*1799 + (4081085<<4))>>11; //1469
        dstV[i] = (dstV[i]*1799 + (4081085<<4))>>11; //1469
    }
}
static void lumRangeToJpeg16_c(int16_t *_dst, int width)
{
    int i;
    int32_t *dst = (int32_t *) _dst;
    for (i = 0; i < width; i++)
        dst[i] = (FFMIN(dst[i],30189<<4)*4769 - (39057361<<2))>>12;
}
static void lumRangeFromJpeg16_c(int16_t *_dst, int width)
{
    int i;
    int32_t *dst = (int32_t *) _dst;
    for (i = 0; i < width; i++)
        dst[i] = (dst[i]*(14071/4) + (33561947<<4)/4)>>12;
}

static void hyscale_fast_c(SwsContext *c, int16_t *dst, int dstWidth,
                           const uint8_t *src, int srcW, int xInc)
{
    int i;
    unsigned int xpos=0;
    for (i=0;i<dstWidth;i++) {
        register unsigned int xx=xpos>>16;
        register unsigned int xalpha=(xpos&0xFFFF)>>9;
        dst[i]= (src[xx]<<7) + (src[xx+1] - src[xx])*xalpha;
        xpos+=xInc;
    }
    for (i=dstWidth-1; (i*xInc)>>16 >=srcW-1; i--)
        dst[i] = src[srcW-1]*128;
}

// *** horizontal scale Y line to temp buffer
static av_always_inline void hyscale(SwsContext *c, int16_t *dst, int dstWidth,
                                     const uint8_t *src_in[4], int srcW, int xInc,
                                     const int16_t *hLumFilter,
                                     const int32_t *hLumFilterPos, int hLumFilterSize,
                                     uint8_t *formatConvBuffer,
                                     uint32_t *pal, int isAlpha)
{
    void (*toYV12)(uint8_t *, const uint8_t *, const uint8_t *, const uint8_t *, int, uint32_t *) = isAlpha ? c->alpToYV12 : c->lumToYV12;
    void (*convertRange)(int16_t *, int) = isAlpha ? NULL : c->lumConvertRange;
    const uint8_t *src = src_in[isAlpha ? 3 : 0];

    if (toYV12) {
        toYV12(formatConvBuffer, src, src_in[1], src_in[2], srcW, pal);
        src= formatConvBuffer;
    } else if (c->readLumPlanar && !isAlpha) {
        c->readLumPlanar(formatConvBuffer, src_in, srcW);
        src = formatConvBuffer;
    }

    if (!c->hyscale_fast) {
        c->hyScale(c, dst, dstWidth, src, hLumFilter, hLumFilterPos, hLumFilterSize);
    } else { // fast bilinear upscale / crap downscale
        c->hyscale_fast(c, dst, dstWidth, src, srcW, xInc);
    }

    if (convertRange)
        convertRange(dst, dstWidth);
}

static void hcscale_fast_c(SwsContext *c, int16_t *dst1, int16_t *dst2,
                           int dstWidth, const uint8_t *src1,
                           const uint8_t *src2, int srcW, int xInc)
{
    int i;
    unsigned int xpos=0;
    for (i=0;i<dstWidth;i++) {
        register unsigned int xx=xpos>>16;
        register unsigned int xalpha=(xpos&0xFFFF)>>9;
        dst1[i]=(src1[xx]*(xalpha^127)+src1[xx+1]*xalpha);
        dst2[i]=(src2[xx]*(xalpha^127)+src2[xx+1]*xalpha);
        xpos+=xInc;
    }
    for (i=dstWidth-1; (i*xInc)>>16 >=srcW-1; i--) {
        dst1[i] = src1[srcW-1]*128;
        dst2[i] = src2[srcW-1]*128;
    }
}

static av_always_inline void hcscale(SwsContext *c, int16_t *dst1, int16_t *dst2, int dstWidth,
                                     const uint8_t *src_in[4],
                                     int srcW, int xInc, const int16_t *hChrFilter,
                                     const int32_t *hChrFilterPos, int hChrFilterSize,
                                     uint8_t *formatConvBuffer, uint32_t *pal)
{
    const uint8_t *src1 = src_in[1], *src2 = src_in[2];
    if (c->chrToYV12) {
        uint8_t *buf2 = formatConvBuffer + FFALIGN(srcW*2+78, 16);
        c->chrToYV12(formatConvBuffer, buf2, src_in[0], src1, src2, srcW, pal);
        src1= formatConvBuffer;
        src2= buf2;
    } else if (c->readChrPlanar) {
        uint8_t *buf2 = formatConvBuffer + FFALIGN(srcW*2+78, 16);
        c->readChrPlanar(formatConvBuffer, buf2, src_in, srcW);
        src1= formatConvBuffer;
        src2= buf2;
    }

    if (!c->hcscale_fast) {
        c->hcScale(c, dst1, dstWidth, src1, hChrFilter, hChrFilterPos, hChrFilterSize);
        c->hcScale(c, dst2, dstWidth, src2, hChrFilter, hChrFilterPos, hChrFilterSize);
    } else { // fast bilinear upscale / crap downscale
        c->hcscale_fast(c, dst1, dst2, dstWidth, src1, src2, srcW, xInc);
    }

    if (c->chrConvertRange)
        c->chrConvertRange(dst1, dst2, dstWidth);
}

#define DEBUG_SWSCALE_BUFFERS 0
#define DEBUG_BUFFERS(...) if (DEBUG_SWSCALE_BUFFERS) av_log(c, AV_LOG_DEBUG, __VA_ARGS__)

static int swScale(SwsContext *c, const uint8_t* src[],
                   int srcStride[], int srcSliceY,
                   int srcSliceH, uint8_t* dst[], int dstStride[])
{
    /* load a few things into local vars to make the code more readable? and faster */
    const int srcW= c->srcW;
    const int dstW= c->dstW;
    const int dstH= c->dstH;
    const int chrDstW= c->chrDstW;
    const int chrSrcW= c->chrSrcW;
    const int lumXInc= c->lumXInc;
    const int chrXInc= c->chrXInc;
    const enum PixelFormat dstFormat= c->dstFormat;
    const int flags= c->flags;
    int32_t *vLumFilterPos= c->vLumFilterPos;
    int32_t *vChrFilterPos= c->vChrFilterPos;
    int32_t *hLumFilterPos= c->hLumFilterPos;
    int32_t *hChrFilterPos= c->hChrFilterPos;
    int16_t *hLumFilter= c->hLumFilter;
    int16_t *hChrFilter= c->hChrFilter;
    int32_t *lumMmxFilter= c->lumMmxFilter;
    int32_t *chrMmxFilter= c->chrMmxFilter;
    const int vLumFilterSize= c->vLumFilterSize;
    const int vChrFilterSize= c->vChrFilterSize;
    const int hLumFilterSize= c->hLumFilterSize;
    const int hChrFilterSize= c->hChrFilterSize;
    int16_t **lumPixBuf= c->lumPixBuf;
    int16_t **chrUPixBuf= c->chrUPixBuf;
    int16_t **chrVPixBuf= c->chrVPixBuf;
    int16_t **alpPixBuf= c->alpPixBuf;
    const int vLumBufSize= c->vLumBufSize;
    const int vChrBufSize= c->vChrBufSize;
    uint8_t *formatConvBuffer= c->formatConvBuffer;
    const int chrSrcSliceY= srcSliceY >> c->chrSrcVSubSample;
    const int chrSrcSliceH= -((-srcSliceH) >> c->chrSrcVSubSample);
    int lastDstY;
    uint32_t *pal=c->pal_yuv;
    int should_dither= isNBPS(c->srcFormat) || is16BPS(c->srcFormat);

    yuv2planar1_fn yuv2plane1 = c->yuv2plane1;
    yuv2planarX_fn yuv2planeX = c->yuv2planeX;
    yuv2interleavedX_fn yuv2nv12cX = c->yuv2nv12cX;
    yuv2packed1_fn yuv2packed1 = c->yuv2packed1;
    yuv2packed2_fn yuv2packed2 = c->yuv2packed2;
    yuv2packedX_fn yuv2packedX = c->yuv2packedX;

    /* vars which will change and which we need to store back in the context */
    int dstY= c->dstY;
    int lumBufIndex= c->lumBufIndex;
    int chrBufIndex= c->chrBufIndex;
    int lastInLumBuf= c->lastInLumBuf;
    int lastInChrBuf= c->lastInChrBuf;

    if (isPacked(c->srcFormat)) {
        src[0]=
        src[1]=
        src[2]=
        src[3]= src[0];
        srcStride[0]=
        srcStride[1]=
        srcStride[2]=
        srcStride[3]= srcStride[0];
    }
    srcStride[1]<<= c->vChrDrop;
    srcStride[2]<<= c->vChrDrop;

    DEBUG_BUFFERS("swScale() %p[%d] %p[%d] %p[%d] %p[%d] -> %p[%d] %p[%d] %p[%d] %p[%d]\n",
                  src[0], srcStride[0], src[1], srcStride[1], src[2], srcStride[2], src[3], srcStride[3],
                  dst[0], dstStride[0], dst[1], dstStride[1], dst[2], dstStride[2], dst[3], dstStride[3]);
    DEBUG_BUFFERS("srcSliceY: %d srcSliceH: %d dstY: %d dstH: %d\n",
                   srcSliceY,    srcSliceH,    dstY,    dstH);
    DEBUG_BUFFERS("vLumFilterSize: %d vLumBufSize: %d vChrFilterSize: %d vChrBufSize: %d\n",
                   vLumFilterSize,    vLumBufSize,    vChrFilterSize,    vChrBufSize);

    if (dstStride[0]%16 !=0 || dstStride[1]%16 !=0 || dstStride[2]%16 !=0 || dstStride[3]%16 != 0) {
        static int warnedAlready=0; //FIXME move this into the context perhaps
        if (flags & SWS_PRINT_INFO && !warnedAlready) {
            av_log(c, AV_LOG_WARNING, "Warning: dstStride is not aligned!\n"
                   "         ->cannot do aligned memory accesses anymore\n");
            warnedAlready=1;
        }
    }

    if ((int)dst[0]%16 || (int)dst[1]%16 || (int)dst[2]%16 || (int)src[0]%16 || (int)src[1]%16 || (int)src[2]%16
        || dstStride[0]%16 || dstStride[1]%16 || dstStride[2]%16 || dstStride[3]%16
        || srcStride[0]%16 || srcStride[1]%16 || srcStride[2]%16 || srcStride[3]%16
    ) {
        static int warnedAlready=0;
        int cpu_flags = av_get_cpu_flags();
        if (HAVE_MMX2 && (cpu_flags & AV_CPU_FLAG_SSE2) && !warnedAlready){
            av_log(c, AV_LOG_WARNING, "Warning: data is not aligned! This can lead to a speedloss\n");
            warnedAlready=1;
        }
    }

    /* Note the user might start scaling the picture in the middle so this
       will not get executed. This is not really intended but works
       currently, so people might do it. */
    if (srcSliceY ==0) {
        lumBufIndex=-1;
        chrBufIndex=-1;
        dstY=0;
        lastInLumBuf= -1;
        lastInChrBuf= -1;
    }

    if (!should_dither) {
        c->chrDither8 = c->lumDither8 = ff_sws_pb_64;
    }
    lastDstY= dstY;

    for (;dstY < dstH; dstY++) {
        const int chrDstY= dstY>>c->chrDstVSubSample;
        uint8_t *dest[4] = {
            dst[0] + dstStride[0] * dstY,
            dst[1] + dstStride[1] * chrDstY,
            dst[2] + dstStride[2] * chrDstY,
            (CONFIG_SWSCALE_ALPHA && alpPixBuf) ? dst[3] + dstStride[3] * dstY : NULL,
        };
        int use_mmx_vfilter= c->use_mmx_vfilter;

        const int firstLumSrcY= FFMAX(1 - vLumFilterSize, vLumFilterPos[dstY]); //First line needed as input
        const int firstLumSrcY2= FFMAX(1 - vLumFilterSize, vLumFilterPos[FFMIN(dstY | ((1<<c->chrDstVSubSample) - 1), dstH-1)]);
        const int firstChrSrcY= FFMAX(1 - vChrFilterSize, vChrFilterPos[chrDstY]); //First line needed as input

        // Last line needed as input
        int lastLumSrcY  = FFMIN(c->srcH,    firstLumSrcY  + vLumFilterSize) - 1;
        int lastLumSrcY2 = FFMIN(c->srcH,    firstLumSrcY2 + vLumFilterSize) - 1;
        int lastChrSrcY  = FFMIN(c->chrSrcH, firstChrSrcY  + vChrFilterSize) - 1;
        int enough_lines;

        //handle holes (FAST_BILINEAR & weird filters)
        if (firstLumSrcY > lastInLumBuf) lastInLumBuf= firstLumSrcY-1;
        if (firstChrSrcY > lastInChrBuf) lastInChrBuf= firstChrSrcY-1;
        assert(firstLumSrcY >= lastInLumBuf - vLumBufSize + 1);
        assert(firstChrSrcY >= lastInChrBuf - vChrBufSize + 1);

        DEBUG_BUFFERS("dstY: %d\n", dstY);
        DEBUG_BUFFERS("\tfirstLumSrcY: %d lastLumSrcY: %d lastInLumBuf: %d\n",
                         firstLumSrcY,    lastLumSrcY,    lastInLumBuf);
        DEBUG_BUFFERS("\tfirstChrSrcY: %d lastChrSrcY: %d lastInChrBuf: %d\n",
                         firstChrSrcY,    lastChrSrcY,    lastInChrBuf);

        // Do we have enough lines in this slice to output the dstY line
        enough_lines = lastLumSrcY2 < srcSliceY + srcSliceH && lastChrSrcY < -((-srcSliceY - srcSliceH)>>c->chrSrcVSubSample);

        if (!enough_lines) {
            lastLumSrcY = srcSliceY + srcSliceH - 1;
            lastChrSrcY = chrSrcSliceY + chrSrcSliceH - 1;
            DEBUG_BUFFERS("buffering slice: lastLumSrcY %d lastChrSrcY %d\n",
                                            lastLumSrcY, lastChrSrcY);
        }

        //Do horizontal scaling
        while(lastInLumBuf < lastLumSrcY) {
            const uint8_t *src1[4] = {
                src[0] + (lastInLumBuf + 1 - srcSliceY) * srcStride[0],
                src[1] + (lastInLumBuf + 1 - srcSliceY) * srcStride[1],
                src[2] + (lastInLumBuf + 1 - srcSliceY) * srcStride[2],
                src[3] + (lastInLumBuf + 1 - srcSliceY) * srcStride[3],
            };
            lumBufIndex++;
            assert(lumBufIndex < 2*vLumBufSize);
            assert(lastInLumBuf + 1 - srcSliceY < srcSliceH);
            assert(lastInLumBuf + 1 - srcSliceY >= 0);
            hyscale(c, lumPixBuf[ lumBufIndex ], dstW, src1, srcW, lumXInc,
                    hLumFilter, hLumFilterPos, hLumFilterSize,
                    formatConvBuffer,
                    pal, 0);
            if (CONFIG_SWSCALE_ALPHA && alpPixBuf)
                hyscale(c, alpPixBuf[ lumBufIndex ], dstW, src1, srcW,
                        lumXInc, hLumFilter, hLumFilterPos, hLumFilterSize,
                        formatConvBuffer,
                        pal, 1);
            lastInLumBuf++;
            DEBUG_BUFFERS("\t\tlumBufIndex %d: lastInLumBuf: %d\n",
                               lumBufIndex,    lastInLumBuf);
        }
        while(lastInChrBuf < lastChrSrcY) {
            const uint8_t *src1[4] = {
                src[0] + (lastInChrBuf + 1 - chrSrcSliceY) * srcStride[0],
                src[1] + (lastInChrBuf + 1 - chrSrcSliceY) * srcStride[1],
                src[2] + (lastInChrBuf + 1 - chrSrcSliceY) * srcStride[2],
                src[3] + (lastInChrBuf + 1 - chrSrcSliceY) * srcStride[3],
            };
            chrBufIndex++;
            assert(chrBufIndex < 2*vChrBufSize);
            assert(lastInChrBuf + 1 - chrSrcSliceY < (chrSrcSliceH));
            assert(lastInChrBuf + 1 - chrSrcSliceY >= 0);
            //FIXME replace parameters through context struct (some at least)

            if (c->needs_hcscale)
                hcscale(c, chrUPixBuf[chrBufIndex], chrVPixBuf[chrBufIndex],
                          chrDstW, src1, chrSrcW, chrXInc,
                          hChrFilter, hChrFilterPos, hChrFilterSize,
                          formatConvBuffer, pal);
            lastInChrBuf++;
            DEBUG_BUFFERS("\t\tchrBufIndex %d: lastInChrBuf: %d\n",
                               chrBufIndex,    lastInChrBuf);
        }
        //wrap buf index around to stay inside the ring buffer
        if (lumBufIndex >= vLumBufSize) lumBufIndex-= vLumBufSize;
        if (chrBufIndex >= vChrBufSize) chrBufIndex-= vChrBufSize;
        if (!enough_lines)
            break; //we can't output a dstY line so let's try with the next slice

#if HAVE_MMX
        updateMMXDitherTables(c, dstY, lumBufIndex, chrBufIndex, lastInLumBuf, lastInChrBuf);
#endif
        if (should_dither) {
            c->chrDither8 = dither_8x8_128[chrDstY & 7];
            c->lumDither8 = dither_8x8_128[dstY & 7];
        }
        if (dstY >= dstH-2) {
            // hmm looks like we can't use MMX here without overwriting this array's tail
            ff_sws_init_output_funcs(c, &yuv2plane1, &yuv2planeX,  &yuv2nv12cX,
                                     &yuv2packed1, &yuv2packed2, &yuv2packedX);
            use_mmx_vfilter= 0;
        }

        {
            const int16_t **lumSrcPtr= (const int16_t **)(void*) lumPixBuf + lumBufIndex + firstLumSrcY - lastInLumBuf + vLumBufSize;
            const int16_t **chrUSrcPtr= (const int16_t **)(void*) chrUPixBuf + chrBufIndex + firstChrSrcY - lastInChrBuf + vChrBufSize;
            const int16_t **chrVSrcPtr= (const int16_t **)(void*) chrVPixBuf + chrBufIndex + firstChrSrcY - lastInChrBuf + vChrBufSize;
            const int16_t **alpSrcPtr= (CONFIG_SWSCALE_ALPHA && alpPixBuf) ? (const int16_t **)(void*) alpPixBuf + lumBufIndex + firstLumSrcY - lastInLumBuf + vLumBufSize : NULL;
            int16_t *vLumFilter= c->vLumFilter;
            int16_t *vChrFilter= c->vChrFilter;

            if (isPlanarYUV(dstFormat) || (isGray(dstFormat) && !isALPHA(dstFormat))) { //YV12 like
                const int chrSkipMask= (1<<c->chrDstVSubSample)-1;

                vLumFilter +=    dstY * vLumFilterSize;
                vChrFilter += chrDstY * vChrFilterSize;

//                 av_assert0(use_mmx_vfilter != (
//                                yuv2planeX == yuv2planeX_10BE_c
//                             || yuv2planeX == yuv2planeX_10LE_c
//                             || yuv2planeX == yuv2planeX_9BE_c
//                             || yuv2planeX == yuv2planeX_9LE_c
//                             || yuv2planeX == yuv2planeX_16BE_c
//                             || yuv2planeX == yuv2planeX_16LE_c
//                             || yuv2planeX == yuv2planeX_8_c) || !ARCH_X86);

                if(use_mmx_vfilter){
                    vLumFilter= c->lumMmxFilter;
                    vChrFilter= c->chrMmxFilter;
                }

                if (vLumFilterSize == 1) {
                    yuv2plane1(lumSrcPtr[0], dest[0], dstW, c->lumDither8, 0);
                } else {
                    yuv2planeX(vLumFilter, vLumFilterSize,
                               lumSrcPtr, dest[0], dstW, c->lumDither8, 0);
                }

                if (!((dstY&chrSkipMask) || isGray(dstFormat))) {
                    if (yuv2nv12cX) {
                        yuv2nv12cX(c, vChrFilter, vChrFilterSize, chrUSrcPtr, chrVSrcPtr, dest[1], chrDstW);
                    } else if (vChrFilterSize == 1) {
                        yuv2plane1(chrUSrcPtr[0], dest[1], chrDstW, c->chrDither8, 0);
                        yuv2plane1(chrVSrcPtr[0], dest[2], chrDstW, c->chrDither8, 3);
                    } else {
                        yuv2planeX(vChrFilter, vChrFilterSize,
                                   chrUSrcPtr, dest[1], chrDstW, c->chrDither8, 0);
                        yuv2planeX(vChrFilter, vChrFilterSize,
                                   chrVSrcPtr, dest[2], chrDstW, c->chrDither8, use_mmx_vfilter ? (c->uv_offx2 >> 1) : 3);
                    }
                }

                if (CONFIG_SWSCALE_ALPHA && alpPixBuf){
                    if(use_mmx_vfilter){
                        vLumFilter= c->alpMmxFilter;
                    }
                    if (vLumFilterSize == 1) {
                        yuv2plane1(alpSrcPtr[0], dest[3], dstW, c->lumDither8, 0);
                    } else {
                        yuv2planeX(vLumFilter, vLumFilterSize,
                                   alpSrcPtr, dest[3], dstW, c->lumDither8, 0);
                    }
                }
            } else {
                assert(lumSrcPtr  + vLumFilterSize - 1 < lumPixBuf  + vLumBufSize*2);
                assert(chrUSrcPtr + vChrFilterSize - 1 < chrUPixBuf + vChrBufSize*2);
                if (c->yuv2packed1 && vLumFilterSize == 1 && vChrFilterSize <= 2) { //unscaled RGB
                    int chrAlpha = vChrFilterSize == 1 ? 0 : vChrFilter[2 * dstY + 1];
                    yuv2packed1(c, *lumSrcPtr, chrUSrcPtr, chrVSrcPtr,
                                alpPixBuf ? *alpSrcPtr : NULL,
                                dest[0], dstW, chrAlpha, dstY);
                } else if (c->yuv2packed2 && vLumFilterSize == 2 && vChrFilterSize == 2) { //bilinear upscale RGB
                    int lumAlpha = vLumFilter[2 * dstY + 1];
                    int chrAlpha = vChrFilter[2 * dstY + 1];
                    lumMmxFilter[2] =
                    lumMmxFilter[3] = vLumFilter[2 * dstY   ] * 0x10001;
                    chrMmxFilter[2] =
                    chrMmxFilter[3] = vChrFilter[2 * chrDstY] * 0x10001;
                    yuv2packed2(c, lumSrcPtr, chrUSrcPtr, chrVSrcPtr,
                                alpPixBuf ? alpSrcPtr : NULL,
                                dest[0], dstW, lumAlpha, chrAlpha, dstY);
                } else { //general RGB
                    yuv2packedX(c, vLumFilter + dstY * vLumFilterSize,
                                lumSrcPtr, vLumFilterSize,
                                vChrFilter + dstY * vChrFilterSize,
                                chrUSrcPtr, chrVSrcPtr, vChrFilterSize,
                                alpSrcPtr, dest[0], dstW, dstY);
                }
            }
        }
    }

    if (isPlanar(dstFormat) && isALPHA(dstFormat) && !alpPixBuf)
        fillPlane(dst[3], dstStride[3], dstW, dstY-lastDstY, lastDstY, 255);

#if HAVE_MMX2
    if (av_get_cpu_flags() & AV_CPU_FLAG_MMX2)
        __asm__ volatile("sfence":::"memory");
#endif
    emms_c();

    /* store changed local vars back in the context */
    c->dstY= dstY;
    c->lumBufIndex= lumBufIndex;
    c->chrBufIndex= chrBufIndex;
    c->lastInLumBuf= lastInLumBuf;
    c->lastInChrBuf= lastInChrBuf;

    return dstY - lastDstY;
}

static av_cold void sws_init_swScale_c(SwsContext *c)
{
    enum PixelFormat srcFormat = c->srcFormat;

    ff_sws_init_output_funcs(c, &c->yuv2plane1, &c->yuv2planeX,
                             &c->yuv2nv12cX, &c->yuv2packed1,
                             &c->yuv2packed2, &c->yuv2packedX);

    ff_sws_init_input_funcs(c);


    if (c->srcBpc == 8) {
        if (c->dstBpc <= 10) {
            c->hyScale = c->hcScale = hScale8To15_c;
            if (c->flags & SWS_FAST_BILINEAR) {
                c->hyscale_fast = hyscale_fast_c;
                c->hcscale_fast = hcscale_fast_c;
            }
        } else {
            c->hyScale = c->hcScale = hScale8To19_c;
        }
    } else {
        c->hyScale = c->hcScale = c->dstBpc > 10 ? hScale16To19_c : hScale16To15_c;
    }

    if (c->srcRange != c->dstRange && !isAnyRGB(c->dstFormat)) {
        if (c->dstBpc <= 10) {
            if (c->srcRange) {
                c->lumConvertRange = lumRangeFromJpeg_c;
                c->chrConvertRange = chrRangeFromJpeg_c;
            } else {
                c->lumConvertRange = lumRangeToJpeg_c;
                c->chrConvertRange = chrRangeToJpeg_c;
            }
        } else {
            if (c->srcRange) {
                c->lumConvertRange = lumRangeFromJpeg16_c;
                c->chrConvertRange = chrRangeFromJpeg16_c;
            } else {
                c->lumConvertRange = lumRangeToJpeg16_c;
                c->chrConvertRange = chrRangeToJpeg16_c;
            }
        }
    }

    if (!(isGray(srcFormat) || isGray(c->dstFormat) ||
          srcFormat == PIX_FMT_MONOBLACK || srcFormat == PIX_FMT_MONOWHITE))
        c->needs_hcscale = 1;
}

SwsFunc ff_getSwsFunc(SwsContext *c)
{
    sws_init_swScale_c(c);

    if (HAVE_MMX)
        ff_sws_init_swScale_mmx(c);
    if (HAVE_ALTIVEC)
        ff_sws_init_swScale_altivec(c);

    return swScale;
}