PeerStreamer

/*

 * 4XM codec

 * Copyright (c) 2003 Michael Niedermayer

 *

 * 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

 */

/**

 * @file

 * 4XM codec.

 */

#include "libavutil/intreadwrite.h"

#include "avcodec.h"

#include "dsputil.h"

#include "get_bits.h"

#include "bytestream.h"

//#undef NDEBUG

//#include <assert.h>

#define BLOCK_TYPE_VLC_BITS 5

#define ACDC_VLC_BITS 9

#define CFRAME_BUFFER_COUNT 100

static const uint8_t block_type_tab[2][4][8][2]={

 {

  {   //{8,4,2}x{8,4,2}

    { 0,1}, { 2,2}, { 6,3}, {14,4}, {30,5}, {31,5}, { 0,0}

  },{ //{8,4}x1

    { 0,1}, { 0,0}, { 2,2}, { 6,3}, {14,4}, {15,4}, { 0,0}

  },{ //1x{8,4}

    { 0,1}, { 2,2}, { 0,0}, { 6,3}, {14,4}, {15,4}, { 0,0}

  },{ //1x2, 2x1

    { 0,1}, { 0,0}, { 0,0}, { 2,2}, { 6,3}, {14,4}, {15,4}

  }

 },{

  {  //{8,4,2}x{8,4,2}

    { 1,2}, { 4,3}, { 5,3}, {0,2}, {6,3}, {7,3}, {0,0}

  },{//{8,4}x1

    { 1,2}, { 0,0}, { 2,2}, {0,2}, {6,3}, {7,3}, {0,0}

  },{//1x{8,4}

    { 1,2}, { 2,2}, { 0,0}, {0,2}, {6,3}, {7,3}, {0,0}

  },{//1x2, 2x1

    { 1,2}, { 0,0}, { 0,0}, {0,2}, {2,2}, {6,3}, {7,3}

  }

 }

};

static const uint8_t size2index[4][4]={

  {-1, 3, 1, 1},

  { 3, 0, 0, 0},

  { 2, 0, 0, 0},

  { 2, 0, 0, 0},

};

static const int8_t mv[256][2]={

{  0,  0},{  0, -1},{ -1,  0},{  1,  0},{  0,  1},{ -1, -1},{  1, -1},{ -1,  1},

{  1,  1},{  0, -2},{ -2,  0},{  2,  0},{  0,  2},{ -1, -2},{  1, -2},{ -2, -1},

{  2, -1},{ -2,  1},{  2,  1},{ -1,  2},{  1,  2},{ -2, -2},{  2, -2},{ -2,  2},

{  2,  2},{  0, -3},{ -3,  0},{  3,  0},{  0,  3},{ -1, -3},{  1, -3},{ -3, -1},

{  3, -1},{ -3,  1},{  3,  1},{ -1,  3},{  1,  3},{ -2, -3},{  2, -3},{ -3, -2},

{  3, -2},{ -3,  2},{  3,  2},{ -2,  3},{  2,  3},{  0, -4},{ -4,  0},{  4,  0},

{  0,  4},{ -1, -4},{  1, -4},{ -4, -1},{  4, -1},{  4,  1},{ -1,  4},{  1,  4},

{ -3, -3},{ -3,  3},{  3,  3},{ -2, -4},{ -4, -2},{  4, -2},{ -4,  2},{ -2,  4},

{  2,  4},{ -3, -4},{  3, -4},{  4, -3},{ -5,  0},{ -4,  3},{ -3,  4},{  3,  4},

{ -1, -5},{ -5, -1},{ -5,  1},{ -1,  5},{ -2, -5},{  2, -5},{  5, -2},{  5,  2},

{ -4, -4},{ -4,  4},{ -3, -5},{ -5, -3},{ -5,  3},{  3,  5},{ -6,  0},{  0,  6},

{ -6, -1},{ -6,  1},{  1,  6},{  2, -6},{ -6,  2},{  2,  6},{ -5, -4},{  5,  4},

{  4,  5},{ -6, -3},{  6,  3},{ -7,  0},{ -1, -7},{  5, -5},{ -7,  1},{ -1,  7},

{  4, -6},{  6,  4},{ -2, -7},{ -7,  2},{ -3, -7},{  7, -3},{  3,  7},{  6, -5},

{  0, -8},{ -1, -8},{ -7, -4},{ -8,  1},{  4,  7},{  2, -8},{ -2,  8},{  6,  6},

{ -8,  3},{  5, -7},{ -5,  7},{  8, -4},{  0, -9},{ -9, -1},{  1,  9},{  7, -6},

{ -7,  6},{ -5, -8},{ -5,  8},{ -9,  3},{  9, -4},{  7, -7},{  8, -6},{  6,  8},

{ 10,  1},{-10,  2},{  9, -5},{ 10, -3},{ -8, -7},{-10, -4},{  6, -9},{-11,  0},

{ 11,  1},{-11, -2},{ -2, 11},{  7, -9},{ -7,  9},{ 10,  6},{ -4, 11},{  8, -9},

{  8,  9},{  5, 11},{  7,-10},{ 12, -3},{ 11,  6},{ -9, -9},{  8, 10},{  5, 12},

{-11,  7},{ 13,  2},{  6,-12},{ 10,  9},{-11,  8},{ -7, 12},{  0, 14},{ 14, -2},

{ -9, 11},{ -6, 13},{-14, -4},{ -5,-14},{  5, 14},{-15, -1},{-14, -6},{  3,-15},

{ 11,-11},{ -7, 14},{ -5, 15},{  8,-14},{ 15,  6},{  3, 16},{  7,-15},{-16,  5},

{  0, 17},{-16, -6},{-10, 14},{-16,  7},{ 12, 13},{-16,  8},{-17,  6},{-18,  3},

{ -7, 17},{ 15, 11},{ 16, 10},{  2,-19},{  3,-19},{-11,-16},{-18,  8},{-19, -6},

{  2,-20},{-17,-11},{-10,-18},{  8, 19},{-21, -1},{-20,  7},{ -4, 21},{ 21,  5},

{ 15, 16},{  2,-22},{-10,-20},{-22,  5},{ 20,-11},{ -7,-22},{-12, 20},{ 23, -5},

{ 13,-20},{ 24, -2},{-15, 19},{-11, 22},{ 16, 19},{ 23,-10},{-18,-18},{ -9,-24},

{ 24,-10},{ -3, 26},{-23, 13},{-18,-20},{ 17, 21},{ -4, 27},{ 27,  6},{  1,-28},

{-11, 26},{-17,-23},{  7, 28},{ 11,-27},{ 29,  5},{-23,-19},{-28,-11},{-21, 22},

{-30,  7},{-17, 26},{-27, 16},{ 13, 29},{ 19,-26},{ 10,-31},{-14,-30},{ 20,-27},

{-29, 18},{-16,-31},{-28,-22},{ 21,-30},{-25, 28},{ 26,-29},{ 25,-32},{-32,-32}

};

// this is simply the scaled down elementwise product of the standard jpeg quantizer table and the AAN premul table

static const uint8_t dequant_table[64]={

 16, 15, 13, 19, 24, 31, 28, 17,

 17, 23, 25, 31, 36, 63, 45, 21,

 18, 24, 27, 37, 52, 59, 49, 20,

 16, 28, 34, 40, 60, 80, 51, 20,

 18, 31, 48, 66, 68, 86, 56, 21,

 19, 38, 56, 59, 64, 64, 48, 20,

 27, 48, 55, 55, 56, 51, 35, 15,

 20, 35, 34, 32, 31, 22, 15,  8,

};

static VLC block_type_vlc[2][4];

typedef struct CFrameBuffer{

    unsigned int allocated_size;

    unsigned int size;

    int id;

    uint8_t *data;

}CFrameBuffer;

typedef struct FourXContext{

    AVCodecContext *avctx;

    DSPContext dsp;

    AVFrame current_picture, last_picture;

    GetBitContext pre_gb;          ///< ac/dc prefix

    GetBitContext gb;

    const uint8_t *bytestream;

    const uint16_t *wordstream;

    int mv[256];

    VLC pre_vlc;

    int last_dc;

    DECLARE_ALIGNED(16, DCTELEM, block)[6][64];

    void *bitstream_buffer;

    unsigned int bitstream_buffer_size;

    int version;

    CFrameBuffer cfrm[CFRAME_BUFFER_COUNT];

} FourXContext;

#define FIX_1_082392200  70936

#define FIX_1_414213562  92682

#define FIX_1_847759065 121095

#define FIX_2_613125930 171254

#define MULTIPLY(var,const)  (((var)*(const)) >> 16)

static void idct(DCTELEM block[64]){

    int tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;

    int tmp10, tmp11, tmp12, tmp13;

    int z5, z10, z11, z12, z13;

    int i;

    int temp[64];

    for(i=0; i<8; i++){

        tmp10 = block[8*0 + i] + block[8*4 + i];

        tmp11 = block[8*0 + i] - block[8*4 + i];

        tmp13 =          block[8*2 + i] + block[8*6 + i];

        tmp12 = MULTIPLY(block[8*2 + i] - block[8*6 + i], FIX_1_414213562) - tmp13;

        tmp0 = tmp10 + tmp13;

        tmp3 = tmp10 - tmp13;

        tmp1 = tmp11 + tmp12;

        tmp2 = tmp11 - tmp12;

        z13 = block[8*5 + i] + block[8*3 + i];

        z10 = block[8*5 + i] - block[8*3 + i];

        z11 = block[8*1 + i] + block[8*7 + i];

        z12 = block[8*1 + i] - block[8*7 + i];

        tmp7  =          z11 + z13;

        tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562);

        z5    = MULTIPLY(z10 + z12, FIX_1_847759065);

        tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5;

        tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5;

        tmp6 = tmp12 - tmp7;

        tmp5 = tmp11 - tmp6;

        tmp4 = tmp10 + tmp5;

        temp[8*0 + i] = tmp0 + tmp7;

        temp[8*7 + i] = tmp0 - tmp7;

        temp[8*1 + i] = tmp1 + tmp6;

        temp[8*6 + i] = tmp1 - tmp6;

        temp[8*2 + i] = tmp2 + tmp5;

        temp[8*5 + i] = tmp2 - tmp5;

        temp[8*4 + i] = tmp3 + tmp4;

        temp[8*3 + i] = tmp3 - tmp4;

    }

    for(i=0; i<8*8; i+=8){

        tmp10 = temp[0 + i] + temp[4 + i];

        tmp11 = temp[0 + i] - temp[4 + i];

        tmp13 = temp[2 + i] + temp[6 + i];

        tmp12 = MULTIPLY(temp[2 + i] - temp[6 + i], FIX_1_414213562) - tmp13;

        tmp0 = tmp10 + tmp13;

        tmp3 = tmp10 - tmp13;

        tmp1 = tmp11 + tmp12;

        tmp2 = tmp11 - tmp12;

        z13 = temp[5 + i] + temp[3 + i];

        z10 = temp[5 + i] - temp[3 + i];

        z11 = temp[1 + i] + temp[7 + i];

        z12 = temp[1 + i] - temp[7 + i];

        tmp7 = z11 + z13;

        tmp11 = MULTIPLY(z11 - z13, FIX_1_414213562);

        z5 = MULTIPLY(z10 + z12, FIX_1_847759065);

        tmp10 = MULTIPLY(z12, FIX_1_082392200) - z5;

        tmp12 = MULTIPLY(z10, - FIX_2_613125930) + z5;

        tmp6 = tmp12 - tmp7;

        tmp5 = tmp11 - tmp6;

        tmp4 = tmp10 + tmp5;

        block[0 + i] = (tmp0 + tmp7)>>6;

        block[7 + i] = (tmp0 - tmp7)>>6;

        block[1 + i] = (tmp1 + tmp6)>>6;

        block[6 + i] = (tmp1 - tmp6)>>6;

        block[2 + i] = (tmp2 + tmp5)>>6;

        block[5 + i] = (tmp2 - tmp5)>>6;

        block[4 + i] = (tmp3 + tmp4)>>6;

        block[3 + i] = (tmp3 - tmp4)>>6;

    }

}

static av_cold void init_vlcs(FourXContext *f){

    static VLC_TYPE table[8][32][2];

    int i;

    for(i=0; i<8; i++){

        block_type_vlc[0][i].table= table[i];

        block_type_vlc[0][i].table_allocated= 32;

        init_vlc(&block_type_vlc[0][i], BLOCK_TYPE_VLC_BITS, 7,

                 &block_type_tab[0][i][0][1], 2, 1,

                 &block_type_tab[0][i][0][0], 2, 1, INIT_VLC_USE_NEW_STATIC);

    }

}

static void init_mv(FourXContext *f){

    int i;

    for(i=0; i<256; i++){

        if(f->version>1)

            f->mv[i] = mv[i][0]   + mv[i][1]  *f->current_picture.linesize[0]/2;

        else

            f->mv[i] = (i&15) - 8 + ((i>>4)-8)*f->current_picture.linesize[0]/2;

    }

}

#if HAVE_BIGENDIAN

#define LE_CENTRIC_MUL(dst, src, scale, dc) \

    { \

        unsigned tmpval = AV_RN32(src);                 \

        tmpval = (tmpval <<  16) | (tmpval >>  16);     \

        tmpval = tmpval * (scale) + (dc);               \

        tmpval = (tmpval <<  16) | (tmpval >>  16);     \

        AV_WN32A(dst, tmpval);                          \

    }

#else

#define LE_CENTRIC_MUL(dst, src, scale, dc) \

    { \

        unsigned tmpval = AV_RN32(src) * (scale) + (dc); \

        AV_WN32A(dst, tmpval);                           \

    }

#endif

static inline void mcdc(uint16_t *dst, uint16_t *src, int log2w, int h, int stride, int scale, int dc){

   int i;

   dc*= 0x10001;

   switch(log2w){

   case 0:

        for(i=0; i<h; i++){

            dst[0] = scale*src[0] + dc;

            if(scale) src += stride;

            dst += stride;

        }

        break;

    case 1:

        for(i=0; i<h; i++){

            LE_CENTRIC_MUL(dst, src, scale, dc);

            if(scale) src += stride;

            dst += stride;

        }

        break;

    case 2:

        for(i=0; i<h; i++){

            LE_CENTRIC_MUL(dst,     src,     scale, dc);

            LE_CENTRIC_MUL(dst + 2, src + 2, scale, dc);

            if(scale) src += stride;

            dst += stride;

        }

        break;

    case 3:

        for(i=0; i<h; i++){

            LE_CENTRIC_MUL(dst,     src,     scale, dc);

            LE_CENTRIC_MUL(dst + 2, src + 2, scale, dc);

            LE_CENTRIC_MUL(dst + 4, src + 4, scale, dc);

            LE_CENTRIC_MUL(dst + 6, src + 6, scale, dc);

            if(scale) src += stride;

            dst += stride;

        }

        break;

    default: assert(0);

    }

}

static void decode_p_block(FourXContext *f, uint16_t *dst, uint16_t *src, int log2w, int log2h, int stride){

    const int index= size2index[log2h][log2w];

    const int h= 1<<log2h;

    int code= get_vlc2(&f->gb, block_type_vlc[1-(f->version>1)][index].table, BLOCK_TYPE_VLC_BITS, 1);

    uint16_t *start= (uint16_t*)f->last_picture.data[0];

    uint16_t *end= start + stride*(f->avctx->height-h+1) - (1<<log2w);

    assert(code>=0 && code<=6);

    if(code == 0){

        src += f->mv[ *f->bytestream++ ];

        if(start > src || src > end){

            av_log(f->avctx, AV_LOG_ERROR, "mv out of pic\n");

            return;

        }

        mcdc(dst, src, log2w, h, stride, 1, 0);

    }else if(code == 1){

        log2h--;

        decode_p_block(f, dst                  , src                  , log2w, log2h, stride);

        decode_p_block(f, dst + (stride<<log2h), src + (stride<<log2h), log2w, log2h, stride);

    }else if(code == 2){

        log2w--;

        decode_p_block(f, dst             , src             , log2w, log2h, stride);

        decode_p_block(f, dst + (1<<log2w), src + (1<<log2w), log2w, log2h, stride);

    }else if(code == 3 && f->version<2){

        mcdc(dst, src, log2w, h, stride, 1, 0);

    }else if(code == 4){

        src += f->mv[ *f->bytestream++ ];

        if(start > src || src > end){

            av_log(f->avctx, AV_LOG_ERROR, "mv out of pic\n");

            return;

        }

        mcdc(dst, src, log2w, h, stride, 1, av_le2ne16(*f->wordstream++));

    }else if(code == 5){

        mcdc(dst, src, log2w, h, stride, 0, av_le2ne16(*f->wordstream++));

    }else if(code == 6){

        if(log2w){

            dst[0] = av_le2ne16(*f->wordstream++);

            dst[1] = av_le2ne16(*f->wordstream++);

        }else{

            dst[0     ] = av_le2ne16(*f->wordstream++);

            dst[stride] = av_le2ne16(*f->wordstream++);

        }

    }

}

static int decode_p_frame(FourXContext *f, const uint8_t *buf, int length){

    int x, y;

    const int width= f->avctx->width;

    const int height= f->avctx->height;

    uint16_t *src= (uint16_t*)f->last_picture.data[0];

    uint16_t *dst= (uint16_t*)f->current_picture.data[0];

    const int stride= f->current_picture.linesize[0]>>1;

    unsigned int bitstream_size, bytestream_size, wordstream_size, extra;

    if(f->version>1){

        extra=20;

        bitstream_size= AV_RL32(buf+8);

        wordstream_size= AV_RL32(buf+12);

        bytestream_size= AV_RL32(buf+16);

    }else{

        extra=0;

        bitstream_size = AV_RL16(buf-4);

        wordstream_size= AV_RL16(buf-2);

        bytestream_size= FFMAX(length - bitstream_size - wordstream_size, 0);

    }

    if(bitstream_size+ bytestream_size+ wordstream_size + extra != length

       || bitstream_size  > (1<<26)

       || bytestream_size > (1<<26)

       || wordstream_size > (1<<26)

       ){

        av_log(f->avctx, AV_LOG_ERROR, "lengths %d %d %d %d\n", bitstream_size, bytestream_size, wordstream_size,

        bitstream_size+ bytestream_size+ wordstream_size - length);

        return -1;

    }

    av_fast_malloc(&f->bitstream_buffer, &f->bitstream_buffer_size, bitstream_size + FF_INPUT_BUFFER_PADDING_SIZE);

    if (!f->bitstream_buffer)

        return AVERROR(ENOMEM);

    f->dsp.bswap_buf(f->bitstream_buffer, (const uint32_t*)(buf + extra), bitstream_size/4);

    init_get_bits(&f->gb, f->bitstream_buffer, 8*bitstream_size);

    f->wordstream= (const uint16_t*)(buf + extra + bitstream_size);

    f->bytestream= buf + extra + bitstream_size + wordstream_size;

    init_mv(f);

    for(y=0; y<height; y+=8){

        for(x=0; x<width; x+=8){

            decode_p_block(f, dst + x, src + x, 3, 3, stride);

        }

        src += 8*stride;

        dst += 8*stride;

    }

    if(   bitstream_size != (get_bits_count(&f->gb)+31)/32*4

       || (((const char*)f->wordstream - (const char*)buf + 2)&~2) != extra + bitstream_size + wordstream_size

       || (((const char*)f->bytestream - (const char*)buf + 3)&~3) != extra + bitstream_size + wordstream_size + bytestream_size)

        av_log(f->avctx, AV_LOG_ERROR, " %d %td %td bytes left\n",

            bitstream_size - (get_bits_count(&f->gb)+31)/32*4,

            -(((const char*)f->bytestream - (const char*)buf + 3)&~3) + (extra + bitstream_size + wordstream_size + bytestream_size),

            -(((const char*)f->wordstream - (const char*)buf + 2)&~2) + (extra + bitstream_size + wordstream_size)

        );

    return 0;

}

/**

 * decode block and dequantize.

 * Note this is almost identical to MJPEG.

 */

static int decode_i_block(FourXContext *f, DCTELEM *block){

    int code, i, j, level, val;

    /* DC coef */

    val = get_vlc2(&f->pre_gb, f->pre_vlc.table, ACDC_VLC_BITS, 3);

    if (val>>4){

        av_log(f->avctx, AV_LOG_ERROR, "error dc run != 0\n");

    }

    if(val)

        val = get_xbits(&f->gb, val);

    val = val * dequant_table[0] + f->last_dc;

    f->last_dc =

    block[0] = val;

    /* AC coefs */

    i = 1;

    for(;;) {

        code = get_vlc2(&f->pre_gb, f->pre_vlc.table, ACDC_VLC_BITS, 3);

        /* EOB */

        if (code == 0)

            break;

        if (code == 0xf0) {

            i += 16;

        } else {

            level = get_xbits(&f->gb, code & 0xf);

            i += code >> 4;

            if (i >= 64) {

                av_log(f->avctx, AV_LOG_ERROR, "run %d oveflow\n", i);

                return 0;

            }

            j= ff_zigzag_direct[i];

            block[j] = level * dequant_table[j];

            i++;

            if (i >= 64)

                break;

        }

    }

    return 0;

}

static inline void idct_put(FourXContext *f, int x, int y){

    DCTELEM (*block)[64]= f->block;

    int stride= f->current_picture.linesize[0]>>1;

    int i;

    uint16_t *dst = ((uint16_t*)f->current_picture.data[0]) + y * stride + x;

    for(i=0; i<4; i++){

        block[i][0] += 0x80*8*8;

        idct(block[i]);

    }

    if(!(f->avctx->flags&CODEC_FLAG_GRAY)){

        for(i=4; i<6; i++) idct(block[i]);

    }

/* Note transform is:

y= ( 1b + 4g + 2r)/14

cb=( 3b - 2g - 1r)/14

cr=(-1b - 4g + 5r)/14

*/

    for(y=0; y<8; y++){

        for(x=0; x<8; x++){

            DCTELEM *temp= block[(x>>2) + 2*(y>>2)] + 2*(x&3) + 2*8*(y&3); //FIXME optimize

            int cb= block[4][x + 8*y];

            int cr= block[5][x + 8*y];

            int cg= (cb + cr)>>1;

            int y;

            cb+=cb;

            y = temp[0];

            dst[0       ]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);

            y = temp[1];

            dst[1       ]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);

            y = temp[8];

            dst[  stride]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);

            y = temp[9];

            dst[1+stride]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);

            dst += 2;

        }

        dst += 2*stride - 2*8;

    }

}

static int decode_i_mb(FourXContext *f){

    int i;

    f->dsp.clear_blocks(f->block[0]);

    for(i=0; i<6; i++){

        if(decode_i_block(f, f->block[i]) < 0)

            return -1;

    }

    return 0;

}

static const uint8_t *read_huffman_tables(FourXContext *f, const uint8_t * const buf){

    int frequency[512];

    uint8_t flag[512];

    int up[512];

    uint8_t len_tab[257];

    int bits_tab[257];

    int start, end;

    const uint8_t *ptr= buf;

    int j;

    memset(frequency, 0, sizeof(frequency));

    memset(up, -1, sizeof(up));

    start= *ptr++;

    end= *ptr++;

    for(;;){

        int i;

        for(i=start; i<=end; i++){

            frequency[i]= *ptr++;

        }

        start= *ptr++;

        if(start==0) break;

        end= *ptr++;

    }

    frequency[256]=1;

    while((ptr - buf)&3) ptr++; // 4byte align

    for(j=257; j<512; j++){

        int min_freq[2]= {256*256, 256*256};

        int smallest[2]= {0, 0};

        int i;

        for(i=0; i<j; i++){

            if(frequency[i] == 0) continue;

            if(frequency[i] < min_freq[1]){

                if(frequency[i] < min_freq[0]){

                    min_freq[1]= min_freq[0]; smallest[1]= smallest[0];

                    min_freq[0]= frequency[i];smallest[0]= i;

                }else{

                    min_freq[1]= frequency[i];smallest[1]= i;

                }

            }

        }

        if(min_freq[1] == 256*256) break;

        frequency[j]= min_freq[0] + min_freq[1];

        flag[ smallest[0] ]= 0;

        flag[ smallest[1] ]= 1;

        up[ smallest[0] ]=

        up[ smallest[1] ]= j;

        frequency[ smallest[0] ]= frequency[ smallest[1] ]= 0;

    }

    for(j=0; j<257; j++){

        int node;

        int len=0;

        int bits=0;

        for(node= j; up[node] != -1; node= up[node]){

            bits += flag[node]<<len;

            len++;

            if(len > 31) av_log(f->avctx, AV_LOG_ERROR, "vlc length overflow\n"); //can this happen at all ?

        }

        bits_tab[j]= bits;

        len_tab[j]= len;

    }

    init_vlc(&f->pre_vlc, ACDC_VLC_BITS, 257,

             len_tab , 1, 1,

             bits_tab, 4, 4, 0);

    return ptr;

}

static int mix(int c0, int c1){

    int blue = 2*(c0&0x001F) + (c1&0x001F);

    int green= (2*(c0&0x03E0) + (c1&0x03E0))>>5;

    int red  = 2*(c0>>10) + (c1>>10);

    return red/3*1024 + green/3*32 + blue/3;

}

static int decode_i2_frame(FourXContext *f, const uint8_t *buf, int length){

    int x, y, x2, y2;

    const int width= f->avctx->width;

    const int height= f->avctx->height;

    uint16_t *dst= (uint16_t*)f->current_picture.data[0];

    const int stride= f->current_picture.linesize[0]>>1;

    for(y=0; y<height; y+=16){

        for(x=0; x<width; x+=16){

            unsigned int color[4], bits;

            memset(color, 0, sizeof(color));

//warning following is purely guessed ...

            color[0]= bytestream_get_le16(&buf);

            color[1]= bytestream_get_le16(&buf);

            if(color[0]&0x8000) av_log(NULL, AV_LOG_ERROR, "unk bit 1\n");

            if(color[1]&0x8000) av_log(NULL, AV_LOG_ERROR, "unk bit 2\n");

            color[2]= mix(color[0], color[1]);

            color[3]= mix(color[1], color[0]);

            bits= bytestream_get_le32(&buf);

            for(y2=0; y2<16; y2++){

                for(x2=0; x2<16; x2++){

                    int index= 2*(x2>>2) + 8*(y2>>2);

                    dst[y2*stride+x2]= color[(bits>>index)&3];

                }

            }

            dst+=16;

        }

        dst += 16*stride - width;

    }

    return 0;

}

static int decode_i_frame(FourXContext *f, const uint8_t *buf, int length){

    int x, y;

    const int width= f->avctx->width;

    const int height= f->avctx->height;

    uint16_t *dst= (uint16_t*)f->current_picture.data[0];

    const int stride= f->current_picture.linesize[0]>>1;

    const unsigned int bitstream_size= AV_RL32(buf);

    const int token_count av_unused = AV_RL32(buf + bitstream_size + 8);

    unsigned int prestream_size= 4*AV_RL32(buf + bitstream_size + 4);

    const uint8_t *prestream= buf + bitstream_size + 12;

    if(prestream_size + bitstream_size + 12 != length

       || bitstream_size > (1<<26)

       || prestream_size > (1<<26)){

        av_log(f->avctx, AV_LOG_ERROR, "size mismatch %d %d %d\n", prestream_size, bitstream_size, length);

        return -1;

    }

    prestream= read_huffman_tables(f, prestream);

    init_get_bits(&f->gb, buf + 4, 8*bitstream_size);

    prestream_size= length + buf - prestream;

    av_fast_malloc(&f->bitstream_buffer, &f->bitstream_buffer_size, prestream_size + FF_INPUT_BUFFER_PADDING_SIZE);

    if (!f->bitstream_buffer)

        return AVERROR(ENOMEM);

    f->dsp.bswap_buf(f->bitstream_buffer, (const uint32_t*)prestream, prestream_size/4);

    init_get_bits(&f->pre_gb, f->bitstream_buffer, 8*prestream_size);

    f->last_dc= 0*128*8*8;

    for(y=0; y<height; y+=16){

        for(x=0; x<width; x+=16){

            if(decode_i_mb(f) < 0)

                return -1;

            idct_put(f, x, y);

        }

        dst += 16*stride;

    }

    if(get_vlc2(&f->pre_gb, f->pre_vlc.table, ACDC_VLC_BITS, 3) != 256)

        av_log(f->avctx, AV_LOG_ERROR, "end mismatch\n");

    return 0;

}

static int decode_frame(AVCodecContext *avctx,

                        void *data, int *data_size,

                        AVPacket *avpkt)

{

    const uint8_t *buf = avpkt->data;

    int buf_size = avpkt->size;

    FourXContext * const f = avctx->priv_data;

    AVFrame *picture = data;

    AVFrame *p, temp;

    int i, frame_4cc, frame_size;

    frame_4cc= AV_RL32(buf);

    if(buf_size != AV_RL32(buf+4)+8 || buf_size < 20){

        av_log(f->avctx, AV_LOG_ERROR, "size mismatch %d %d\n", buf_size, AV_RL32(buf+4));

    }

    if(frame_4cc == AV_RL32("cfrm")){

        int free_index=-1;

        const int data_size= buf_size - 20;

        const int id= AV_RL32(buf+12);

        const int whole_size= AV_RL32(buf+16);

        CFrameBuffer *cfrm;

        for(i=0; i<CFRAME_BUFFER_COUNT; i++){

            if(f->cfrm[i].id && f->cfrm[i].id < avctx->frame_number)

                av_log(f->avctx, AV_LOG_ERROR, "lost c frame %d\n", f->cfrm[i].id);

        }

        for(i=0; i<CFRAME_BUFFER_COUNT; i++){

            if(f->cfrm[i].id   == id) break;

            if(f->cfrm[i].size == 0 ) free_index= i;

        }

        if(i>=CFRAME_BUFFER_COUNT){

            i= free_index;

            f->cfrm[i].id= id;

        }

        cfrm= &f->cfrm[i];

        cfrm->data= av_fast_realloc(cfrm->data, &cfrm->allocated_size, cfrm->size + data_size + FF_INPUT_BUFFER_PADDING_SIZE);

        if(!cfrm->data){ //explicit check needed as memcpy below might not catch a NULL

            av_log(f->avctx, AV_LOG_ERROR, "realloc falure");

            return -1;

        }

        memcpy(cfrm->data + cfrm->size, buf+20, data_size);

        cfrm->size += data_size;

        if(cfrm->size >= whole_size){

            buf= cfrm->data;

            frame_size= cfrm->size;

            if(id != avctx->frame_number){

                av_log(f->avctx, AV_LOG_ERROR, "cframe id mismatch %d %d\n", id, avctx->frame_number);

            }

            cfrm->size= cfrm->id= 0;

            frame_4cc= AV_RL32("pfrm");

        }else

            return buf_size;

    }else{

        buf= buf + 12;

        frame_size= buf_size - 12;

    }

    temp= f->current_picture;

    f->current_picture= f->last_picture;

    f->last_picture= temp;

    p= &f->current_picture;

    avctx->coded_frame= p;

    avctx->flags |= CODEC_FLAG_EMU_EDGE; // alternatively we would have to use our own buffer management

    p->reference= 1;

    if (avctx->reget_buffer(avctx, p) < 0) {

        av_log(avctx, AV_LOG_ERROR, "reget_buffer() failed\n");

        return -1;

    }

    if(frame_4cc == AV_RL32("ifr2")){

        p->pict_type= AV_PICTURE_TYPE_I;

        if(decode_i2_frame(f, buf-4, frame_size) < 0)

            return -1;

    }else if(frame_4cc == AV_RL32("ifrm")){

        p->pict_type= AV_PICTURE_TYPE_I;

        if(decode_i_frame(f, buf, frame_size) < 0)

            return -1;

    }else if(frame_4cc == AV_RL32("pfrm") || frame_4cc == AV_RL32("pfr2")){

        if(!f->last_picture.data[0]){

            f->last_picture.reference= 1;

            if(avctx->get_buffer(avctx, &f->last_picture) < 0){

                av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");

                return -1;

            }

        }

        p->pict_type= AV_PICTURE_TYPE_P;

        if(decode_p_frame(f, buf, frame_size) < 0)

            return -1;

    }else if(frame_4cc == AV_RL32("snd_")){

        av_log(avctx, AV_LOG_ERROR, "ignoring snd_ chunk length:%d\n", buf_size);

    }else{

        av_log(avctx, AV_LOG_ERROR, "ignoring unknown chunk length:%d\n", buf_size);

    }

    p->key_frame= p->pict_type == AV_PICTURE_TYPE_I;

    *picture= *p;

    *data_size = sizeof(AVPicture);

    emms_c();

    return buf_size;

}

static av_cold void common_init(AVCodecContext *avctx){

    FourXContext * const f = avctx->priv_data;

    dsputil_init(&f->dsp, avctx);

    f->avctx= avctx;

}

static av_cold int decode_init(AVCodecContext *avctx){

    FourXContext * const f = avctx->priv_data;

    if(avctx->extradata_size != 4 || !avctx->extradata) {

        av_log(avctx, AV_LOG_ERROR, "extradata wrong or missing\n");

        return 1;

    }

    f->version= AV_RL32(avctx->extradata)>>16;

    common_init(avctx);

    init_vlcs(f);

    if(f->version>2) avctx->pix_fmt= PIX_FMT_RGB565;

    else             avctx->pix_fmt= PIX_FMT_BGR555;

    return 0;

}

static av_cold int decode_end(AVCodecContext *avctx){

    FourXContext * const f = avctx->priv_data;

    int i;

    av_freep(&f->bitstream_buffer);

    f->bitstream_buffer_size=0;

    for(i=0; i<CFRAME_BUFFER_COUNT; i++){

        av_freep(&f->cfrm[i].data);

        f->cfrm[i].allocated_size= 0;

    }

    free_vlc(&f->pre_vlc);

    if(f->current_picture.data[0])

        avctx->release_buffer(avctx, &f->current_picture);

    if(f->last_picture.data[0])

        avctx->release_buffer(avctx, &f->last_picture);

    return 0;

}

AVCodec ff_fourxm_decoder = {

    "4xm",

    AVMEDIA_TYPE_VIDEO,

    CODEC_ID_4XM,

    sizeof(FourXContext),

    decode_init,

    NULL,

    decode_end,

    decode_frame,

    CODEC_CAP_DR1,

    .long_name = NULL_IF_CONFIG_SMALL("4X Movie"),

};