mpeg12.c

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                s->qscale = get_qscale(s);

            /* motion vectors */
            s->mv_dir= (mb_type>>13)&3;
            dprintf(s->avctx, "motion_type=%d\n", motion_type);
            switch(motion_type) {
            case MT_FRAME: /* or MT_16X8 */
                if (s->picture_structure == PICT_FRAME) {
                    mb_type |= MB_TYPE_16x16;
                    s->mv_type = MV_TYPE_16X16;
                    for(i=0;i<2;i++) {
                        if (USES_LIST(mb_type, i)) {
                            /* MT_FRAME */
                            s->mv[i][0][0]= s->last_mv[i][0][0]= s->last_mv[i][1][0] =
                                mpeg_decode_motion(s, s->mpeg_f_code[i][0], s->last_mv[i][0][0]);
                            s->mv[i][0][1]= s->last_mv[i][0][1]= s->last_mv[i][1][1] =
                                mpeg_decode_motion(s, s->mpeg_f_code[i][1], s->last_mv[i][0][1]);
                            /* full_pel: only for mpeg1 */
                            if (s->full_pel[i]){
                                s->mv[i][0][0] <<= 1;
                                s->mv[i][0][1] <<= 1;
                            }
                        }
                    }
                } else {
                    mb_type |= MB_TYPE_16x8 | MB_TYPE_INTERLACED;
                    s->mv_type = MV_TYPE_16X8;
                    for(i=0;i<2;i++) {
                        if (USES_LIST(mb_type, i)) {
                            /* MT_16X8 */
                            for(j=0;j<2;j++) {
                                s->field_select[i][j] = get_bits1(&s->gb);
                                for(k=0;k<2;k++) {
                                    val = mpeg_decode_motion(s, s->mpeg_f_code[i][k],
                                                             s->last_mv[i][j][k]);
                                    s->last_mv[i][j][k] = val;
                                    s->mv[i][j][k] = val;
                                }
                            }
                        }
                    }
                }
                break;
            case MT_FIELD:
                s->mv_type = MV_TYPE_FIELD;
                if (s->picture_structure == PICT_FRAME) {
                    mb_type |= MB_TYPE_16x8 | MB_TYPE_INTERLACED;
                    for(i=0;i<2;i++) {
                        if (USES_LIST(mb_type, i)) {
                            for(j=0;j<2;j++) {
                                s->field_select[i][j] = get_bits1(&s->gb);
                                val = mpeg_decode_motion(s, s->mpeg_f_code[i][0],
                                                         s->last_mv[i][j][0]);
                                s->last_mv[i][j][0] = val;
                                s->mv[i][j][0] = val;
                                dprintf(s->avctx, "fmx=%d\n", val);
                                val = mpeg_decode_motion(s, s->mpeg_f_code[i][1],
                                                         s->last_mv[i][j][1] >> 1);
                                s->last_mv[i][j][1] = val << 1;
                                s->mv[i][j][1] = val;
                                dprintf(s->avctx, "fmy=%d\n", val);
                            }
                        }
                    }
                } else {
                    mb_type |= MB_TYPE_16x16 | MB_TYPE_INTERLACED;
                    for(i=0;i<2;i++) {
                        if (USES_LIST(mb_type, i)) {
                            s->field_select[i][0] = get_bits1(&s->gb);
                            for(k=0;k<2;k++) {
                                val = mpeg_decode_motion(s, s->mpeg_f_code[i][k],
                                                         s->last_mv[i][0][k]);
                                s->last_mv[i][0][k] = val;
                                s->last_mv[i][1][k] = val;
                                s->mv[i][0][k] = val;
                            }
                        }
                    }
                }
                break;
            case MT_DMV:
                s->mv_type = MV_TYPE_DMV;
                for(i=0;i<2;i++) {
                    if (USES_LIST(mb_type, i)) {
                        int dmx, dmy, mx, my, m;
                        mx = mpeg_decode_motion(s, s->mpeg_f_code[i][0],
                                                s->last_mv[i][0][0]);
                        s->last_mv[i][0][0] = mx;
                        s->last_mv[i][1][0] = mx;
                        dmx = get_dmv(s);
                        my = mpeg_decode_motion(s, s->mpeg_f_code[i][1],
                                                s->last_mv[i][0][1] >> 1);
                        dmy = get_dmv(s);


                        s->last_mv[i][0][1] = my<<1;
                        s->last_mv[i][1][1] = my<<1;

                        s->mv[i][0][0] = mx;
                        s->mv[i][0][1] = my;
                        s->mv[i][1][0] = mx;//not used
                        s->mv[i][1][1] = my;//not used

                        if (s->picture_structure == PICT_FRAME) {
                            mb_type |= MB_TYPE_16x16 | MB_TYPE_INTERLACED;

                            //m = 1 + 2 * s->top_field_first;
                            m = s->top_field_first ? 1 : 3;

                            /* top -> top pred */
                            s->mv[i][2][0] = ((mx * m + (mx > 0)) >> 1) + dmx;
                            s->mv[i][2][1] = ((my * m + (my > 0)) >> 1) + dmy - 1;
                            m = 4 - m;
                            s->mv[i][3][0] = ((mx * m + (mx > 0)) >> 1) + dmx;
                            s->mv[i][3][1] = ((my * m + (my > 0)) >> 1) + dmy + 1;
                        } else {
                            mb_type |= MB_TYPE_16x16;

                            s->mv[i][2][0] = ((mx + (mx > 0)) >> 1) + dmx;
                            s->mv[i][2][1] = ((my + (my > 0)) >> 1) + dmy;
                            if(s->picture_structure == PICT_TOP_FIELD)
                                s->mv[i][2][1]--;
                            else
                                s->mv[i][2][1]++;
                        }
                    }
                }
                break;
            default:
                av_log(s->avctx, AV_LOG_ERROR, "00 motion_type at %d %d\n", s->mb_x, s->mb_y);
                return -1;
            }
        }

        s->mb_intra = 0;
        if (HAS_CBP(mb_type)) {
            s->dsp.clear_blocks(s->block[0]);

            cbp = get_vlc2(&s->gb, mb_pat_vlc.table, MB_PAT_VLC_BITS, 1);
            if(mb_block_count > 6){
                 cbp<<= mb_block_count-6;
                 cbp |= get_bits(&s->gb, mb_block_count-6);
                 s->dsp.clear_blocks(s->block[6]);
            }
            if (cbp <= 0){
                av_log(s->avctx, AV_LOG_ERROR, "invalid cbp at %d %d\n", s->mb_x, s->mb_y);
                return -1;
            }

#ifdef HAVE_XVMC
            //on 1 we memcpy blocks in xvmcvideo
            if(s->avctx->xvmc_acceleration > 1){
                XVMC_pack_pblocks(s,cbp);
                if(s->swap_uv){
                    exchange_uv(s);
                }
            }
#endif

            if (s->codec_id == CODEC_ID_MPEG2VIDEO) {
                if(s->flags2 & CODEC_FLAG2_FAST){
                    for(i=0;i<6;i++) {
                        if(cbp & 32) {
                            mpeg2_fast_decode_block_non_intra(s, s->pblocks[i], i);
                        } else {
                            s->block_last_index[i] = -1;
                        }
                        cbp+=cbp;
                    }
                }else{
                    cbp<<= 12-mb_block_count;

                    for(i=0;i<mb_block_count;i++) {
                        if ( cbp & (1<<11) ) {
                            if (mpeg2_decode_block_non_intra(s, s->pblocks[i], i) < 0)
                                return -1;
                        } else {
                            s->block_last_index[i] = -1;
                        }
                        cbp+=cbp;
                    }
                }
            } else {
                if(s->flags2 & CODEC_FLAG2_FAST){
                    for(i=0;i<6;i++) {
                        if (cbp & 32) {
                            mpeg1_fast_decode_block_inter(s, s->pblocks[i], i);
                        } else {
                            s->block_last_index[i] = -1;
                        }
                        cbp+=cbp;
                    }
                }else{
                    for(i=0;i<6;i++) {
                        if (cbp & 32) {
                            if (mpeg1_decode_block_inter(s, s->pblocks[i], i) < 0)
                                return -1;
                        } else {
                            s->block_last_index[i] = -1;
                        }
                        cbp+=cbp;
                    }
                }
            }
        }else{
            for(i=0;i<12;i++)
                s->block_last_index[i] = -1;
        }
    }

    s->current_picture.mb_type[ s->mb_x + s->mb_y*s->mb_stride ]= mb_type;

    return 0;
}

/* as h263, but only 17 codes */
static int mpeg_decode_motion(MpegEncContext *s, int fcode, int pred)
{
    int code, sign, val, l, shift;

    code = get_vlc2(&s->gb, mv_vlc.table, MV_VLC_BITS, 2);
    if (code == 0) {
        return pred;
    }
    if (code < 0) {
        return 0xffff;
    }

    sign = get_bits1(&s->gb);
    shift = fcode - 1;
    val = code;
    if (shift) {
        val = (val - 1) << shift;
        val |= get_bits(&s->gb, shift);
        val++;
    }
    if (sign)
        val = -val;
    val += pred;

    /* modulo decoding */
    l= INT_BIT - 5 - shift;
    val = (val<<l)>>l;
    return val;
}

static inline int decode_dc(GetBitContext *gb, int component)
{
    int code, diff;

    if (component == 0) {
        code = get_vlc2(gb, dc_lum_vlc.table, DC_VLC_BITS, 2);
    } else {
        code = get_vlc2(gb, dc_chroma_vlc.table, DC_VLC_BITS, 2);
    }
    if (code < 0){
        av_log(NULL, AV_LOG_ERROR, "invalid dc code at\n");
        return 0xffff;
    }
    if (code == 0) {
        diff = 0;
    } else {
        diff = get_xbits(gb, code);
    }
    return diff;
}

static inline int mpeg1_decode_block_intra(MpegEncContext *s,
                               DCTELEM *block,
                               int n)
{
    int level, dc, diff, i, j, run;
    int component;
    RLTable *rl = &ff_rl_mpeg1;
    uint8_t * const scantable= s->intra_scantable.permutated;
    const uint16_t *quant_matrix= s->intra_matrix;
    const int qscale= s->qscale;

    /* DC coef */
    component = (n <= 3 ? 0 : n - 4 + 1);
    diff = decode_dc(&s->gb, component);
    if (diff >= 0xffff)
        return -1;
    dc = s->last_dc[component];
    dc += diff;
    s->last_dc[component] = dc;
    block[0] = dc<<3;
    dprintf(s->avctx, "dc=%d diff=%d\n", dc, diff);
    i = 0;
    {
        OPEN_READER(re, &s->gb);
        /* now quantify & encode AC coefs */
        for(;;) {
            UPDATE_CACHE(re, &s->gb);
            GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TEX_VLC_BITS, 2, 0);

            if(level == 127){
                break;
            } else if(level != 0) {
                i += run;
                j = scantable[i];
                level= (level*qscale*quant_matrix[j])>>4;
                level= (level-1)|1;
                level = (level ^ SHOW_SBITS(re, &s->gb, 1)) - SHOW_SBITS(re, &s->gb, 1);
                LAST_SKIP_BITS(re, &s->gb, 1);
            } else {
                /* escape */
                run = SHOW_UBITS(re, &s->gb, 6)+1; LAST_SKIP_BITS(re, &s->gb, 6);
                UPDATE_CACHE(re, &s->gb);
                level = SHOW_SBITS(re, &s->gb, 8); SKIP_BITS(re, &s->gb, 8);
                if (level == -128) {
                    level = SHOW_UBITS(re, &s->gb, 8) - 256; LAST_SKIP_BITS(re, &s->gb, 8);
                } else if (level == 0) {
                    level = SHOW_UBITS(re, &s->gb, 8)      ; LAST_SKIP_BITS(re, &s->gb, 8);
                }
                i += run;
                j = scantable[i];
                if(level<0){
                    level= -level;
                    level= (level*qscale*quant_matrix[j])>>4;
                    level= (level-1)|1;
                    level= -level;
                }else{
                    level= (level*qscale*quant_matrix[j])>>4;
                    level= (level-1)|1;
                }
            }
            if (i > 63){
                av_log(s->avctx, AV_LOG_ERROR, "ac-tex damaged at %d %d\n", s->mb_x, s->mb_y);
                return -1;
            }

            block[j] = level;
        }
        CLOSE_READER(re, &s->gb);
    }
    s->block_last_index[n] = i;
   return 0;
}

static inline int mpeg1_decode_block_inter(MpegEncContext *s,
                               DCTELEM *block,
                               int n)
{
    int level, i, j, run;
    RLTable *rl = &ff_rl_mpeg1;
    uint8_t * const scantable= s->intra_scantable.permutated;
    const uint16_t *quant_matrix= s->inter_matrix;
    const int qscale= s->qscale;

    {
        OPEN_READER(re, &s->gb);
        i = -1;
        /* special case for the first coef. no need to add a second vlc table */
        UPDATE_CACHE(re, &s->gb);
        if (((int32_t)GET_CACHE(re, &s->gb)) < 0) {
            level= (3*qscale*quant_matrix[0])>>5;
            level= (level-1)|1;
            if(GET_CACHE(re, &s->gb)&0x40000000)
                level= -level;
            block[0] = level;
            i++;
            SKIP_BITS(re, &s->gb, 2);
            if(((int32_t)GET_CACHE(re, &s->gb)) <= (int32_t)0xBFFFFFFF)
                goto end;
        }
#if MIN_CACHE_BITS < 19
        UPDATE_CACHE(re, &s->gb);
#endif
        /* now quantify & encode AC coefs */
        for(;;) {
            GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TEX_VLC_BITS, 2, 0);

            if(level != 0) {
                i += run;
                j = scantable[i];
                level= ((level*2+1)*qscale*quant_matrix[j])>>5;
                level= (level-1)|1;
                level = (level ^ SHOW_SBITS(re, &s->gb, 1)) - SHOW_SBITS(re, &s->gb, 1);
                SKIP_BITS(re, &s->gb, 1);