func: int ff_h263_decode_mb(MpegEncContext *s,
                        int16_t block[6][64])
  {
      int cbpc, cbpy, i, cbp, pred_x, pred_y, mx, my, dquant;
      int16_t *mot_val;
      const int xy= s->mb_x + s->mb_y * s->mb_stride;
      int cbpb = 0, pb_mv_count = 0;
      av_assert2(!s->h263_pred);
      if (s->pict_type == AV_PICTURE_TYPE_P) {
          do{
              if (get_bits1(&s->gb)) {
                  /* skip mb */
                  s->mb_intra = 0;
                  for(i=0;i<6;i++)
                      s->block_last_index[i] = -1;
                  s->mv_dir = MV_DIR_FORWARD;
                  s->mv_type = MV_TYPE_16X16;
                  s->current_picture.mb_type[xy] = MB_TYPE_SKIP | MB_TYPE_16x16 | MB_TYPE_L0;
                  s->mv[0][0][0] = 0;
                  s->mv[0][0][1] = 0;
                  s->mb_skipped = !(s->obmc | s->loop_filter);
                  goto end;
              cbpc = get_vlc2(&s->gb, ff_h263_inter_MCBPC_vlc.table, INTER_MCBPC_VLC_BITS, 2);
              if (cbpc < 0){
                  av_log(s->avctx, AV_LOG_ERROR, "cbpc damaged at %d %d\n", s->mb_x, s->mb_y);
          }while(cbpc == 20);
          s->bdsp.clear_blocks(s->block[0]);
          dquant = cbpc & 8;
          s->mb_intra = ((cbpc & 4) != 0);
          if (s->mb_intra) goto intra;
          if(s->pb_frame && get_bits1(&s->gb))
              pb_mv_count = h263_get_modb(&s->gb, s->pb_frame, &cbpb);
          cbpy = get_vlc2(&s->gb, ff_h263_cbpy_vlc.table, CBPY_VLC_BITS, 1);
          if(s->alt_inter_vlc==0 || (cbpc & 3)!=3)
              cbpy ^= 0xF;
          cbp = (cbpc & 3) | (cbpy << 2);
          if (dquant) {
              h263_decode_dquant(s);
          s->mv_dir = MV_DIR_FORWARD;
          if ((cbpc & 16) == 0) {
              s->current_picture.mb_type[xy] = MB_TYPE_16x16 | MB_TYPE_L0;
              /* 16x16 motion prediction */
              s->mv_type = MV_TYPE_16X16;
              ff_h263_pred_motion(s, 0, 0, &pred_x, &pred_y);
              if (s->umvplus)
                 mx = h263p_decode_umotion(s, pred_x);
              else
                 mx = ff_h263_decode_motion(s, pred_x, 1);
              if (mx >= 0xffff)
              if (s->umvplus)
                 my = h263p_decode_umotion(s, pred_y);
              else
                 my = ff_h263_decode_motion(s, pred_y, 1);
              if (my >= 0xffff)
              s->mv[0][0][0] = mx;
              s->mv[0][0][1] = my;
              if (s->umvplus && (mx - pred_x) == 1 && (my - pred_y) == 1)
                 skip_bits1(&s->gb); /* Bit stuffing to prevent PSC */
          } else {
              s->current_picture.mb_type[xy] = MB_TYPE_8x8 | MB_TYPE_L0;
              s->mv_type = MV_TYPE_8X8;
              for(i=0;i<4;i++) {
                  mot_val = ff_h263_pred_motion(s, i, 0, &pred_x, &pred_y);
                  if (s->umvplus)
                      mx = h263p_decode_umotion(s, pred_x);
                  else
                      mx = ff_h263_decode_motion(s, pred_x, 1);
                  if (mx >= 0xffff)
                  if (s->umvplus)
                      my = h263p_decode_umotion(s, pred_y);
                  else
                      my = ff_h263_decode_motion(s, pred_y, 1);
                  if (my >= 0xffff)
                  s->mv[0][i][0] = mx;
                  s->mv[0][i][1] = my;
                  if (s->umvplus && (mx - pred_x) == 1 && (my - pred_y) == 1)
                    skip_bits1(&s->gb); /* Bit stuffing to prevent PSC */
                  mot_val[0] = mx;
                  mot_val[1] = my;
      } else if(s->pict_type==AV_PICTURE_TYPE_B) {
          int mb_type;
          const int stride= s->b8_stride;
          int16_t *mot_val0 = s->current_picture.motion_val[0][2 * (s->mb_x + s->mb_y * stride)];
          int16_t *mot_val1 = s->current_picture.motion_val[1][2 * (s->mb_x + s->mb_y * stride)];
  //        const int mv_xy= s->mb_x + 1 + s->mb_y * s->mb_stride;
          //FIXME ugly
          mot_val0[0       ]= mot_val0[2       ]= mot_val0[0+2*stride]= mot_val0[2+2*stride]=
          mot_val0[1       ]= mot_val0[3       ]= mot_val0[1+2*stride]= mot_val0[3+2*stride]=
          mot_val1[0       ]= mot_val1[2       ]= mot_val1[0+2*stride]= mot_val1[2+2*stride]=
          mot_val1[1       ]= mot_val1[3       ]= mot_val1[1+2*stride]= mot_val1[3+2*stride]= 0;
          do{
              mb_type= get_vlc2(&s->gb, h263_mbtype_b_vlc.table, H263_MBTYPE_B_VLC_BITS, 2);
              if (mb_type < 0){
                  av_log(s->avctx, AV_LOG_ERROR, "b mb_type damaged at %d %d\n", s->mb_x, s->mb_y);
              mb_type= h263_mb_type_b_map[ mb_type ];
          }while(!mb_type);
          s->mb_intra = IS_INTRA(mb_type);
          if(HAS_CBP(mb_type)){
              s->bdsp.clear_blocks(s->block[0]);
              cbpc = get_vlc2(&s->gb, cbpc_b_vlc.table, CBPC_B_VLC_BITS, 1);
              if(s->mb_intra){
                  dquant = IS_QUANT(mb_type);
                  goto intra;
              cbpy = get_vlc2(&s->gb, ff_h263_cbpy_vlc.table, CBPY_VLC_BITS, 1);
              if (cbpy < 0){
                  av_log(s->avctx, AV_LOG_ERROR, "b cbpy damaged at %d %d\n", s->mb_x, s->mb_y);
              if(s->alt_inter_vlc==0 || (cbpc & 3)!=3)
                  cbpy ^= 0xF;
              cbp = (cbpc & 3) | (cbpy << 2);
          }else
              cbp=0;
          av_assert2(!s->mb_intra);
          if(IS_QUANT(mb_type)){
              h263_decode_dquant(s);
          if(IS_DIRECT(mb_type)){
              s->mv_dir = MV_DIR_FORWARD | MV_DIR_BACKWARD | MV_DIRECT;
              mb_type |= set_direct_mv(s);
          }else{
              s->mv_dir = 0;
              s->mv_type= MV_TYPE_16X16;
  //FIXME UMV
              if(USES_LIST(mb_type, 0)){
                  int16_t *mot_val= ff_h263_pred_motion(s, 0, 0, &pred_x, &pred_y);
                  s->mv_dir = MV_DIR_FORWARD;
                  if (s->umvplus)
                      mx = h263p_decode_umotion(s, pred_x);
                  else
                      mx = ff_h263_decode_motion(s, pred_x, 1);
                  if (mx >= 0xffff)
                  if (s->umvplus)
                      my = h263p_decode_umotion(s, pred_y);
                  else
                      my = ff_h263_decode_motion(s, pred_y, 1);
                  if (my >= 0xffff)
                  if (s->umvplus && (mx - pred_x) == 1 && (my - pred_y) == 1)
                      skip_bits1(&s->gb); /* Bit stuffing to prevent PSC */
                  s->mv[0][0][0] = mx;
                  s->mv[0][0][1] = my;
                  mot_val[0       ]= mot_val[2       ]= mot_val[0+2*stride]= mot_val[2+2*stride]= mx;
                  mot_val[1       ]= mot_val[3       ]= mot_val[1+2*stride]= mot_val[3+2*stride]= my;
              if(USES_LIST(mb_type, 1)){
                  int16_t *mot_val= ff_h263_pred_motion(s, 0, 1, &pred_x, &pred_y);
                  s->mv_dir |= MV_DIR_BACKWARD;
                  if (s->umvplus)
                      mx = h263p_decode_umotion(s, pred_x);
                  else
                      mx = ff_h263_decode_motion(s, pred_x, 1);
                  if (mx >= 0xffff)
                  if (s->umvplus)
                      my = h263p_decode_umotion(s, pred_y);
                  else
                      my = ff_h263_decode_motion(s, pred_y, 1);
                  if (my >= 0xffff)
                  if (s->umvplus && (mx - pred_x) == 1 && (my - pred_y) == 1)
                      skip_bits1(&s->gb); /* Bit stuffing to prevent PSC */
                  s->mv[1][0][0] = mx;
                  s->mv[1][0][1] = my;
                  mot_val[0       ]= mot_val[2       ]= mot_val[0+2*stride]= mot_val[2+2*stride]= mx;
                  mot_val[1       ]= mot_val[3       ]= mot_val[1+2*stride]= mot_val[3+2*stride]= my;
          s->current_picture.mb_type[xy] = mb_type;
      } else { /* I-Frame */
          do{
              cbpc = get_vlc2(&s->gb, ff_h263_intra_MCBPC_vlc.table, INTRA_MCBPC_VLC_BITS, 2);
              if (cbpc < 0){
                  av_log(s->avctx, AV_LOG_ERROR, "I cbpc damaged at %d %d\n", s->mb_x, s->mb_y);
          }while(cbpc == 8);
          s->bdsp.clear_blocks(s->block[0]);
          dquant = cbpc & 4;
          s->mb_intra = 1;
  intra:
          s->current_picture.mb_type[xy] = MB_TYPE_INTRA;
          if (s->h263_aic) {
              s->ac_pred = get_bits1(&s->gb);
              if(s->ac_pred){
                  s->current_picture.mb_type[xy] = MB_TYPE_INTRA | MB_TYPE_ACPRED;
                  s->h263_aic_dir = get_bits1(&s->gb);
          }else
              s->ac_pred = 0;
          if(s->pb_frame && get_bits1(&s->gb))
              pb_mv_count = h263_get_modb(&s->gb, s->pb_frame, &cbpb);
          cbpy = get_vlc2(&s->gb, ff_h263_cbpy_vlc.table, CBPY_VLC_BITS, 1);
          if(cbpy<0){
              av_log(s->avctx, AV_LOG_ERROR, "I cbpy damaged at %d %d\n", s->mb_x, s->mb_y);
          cbp = (cbpc & 3) | (cbpy << 2);
          if (dquant) {
              h263_decode_dquant(s);
          pb_mv_count += !!s->pb_frame;
      while(pb_mv_count--){
          ff_h263_decode_motion(s, 0, 1);
          ff_h263_decode_motion(s, 0, 1);
      /* decode each block */
      for (i = 0; i < 6; i++) {
          if (h263_decode_block(s, block[i], i, cbp&32) < 0)
              return -1;
          cbp+=cbp;
      if(s->pb_frame && h263_skip_b_part(s, cbpb) < 0)
          return -1;
      if(s->obmc && !s->mb_intra){
          if(s->pict_type == AV_PICTURE_TYPE_P && s->mb_x+1<s->mb_width && s->mb_num_left != 1)
              preview_obmc(s);
  end:
          /* per-MB end of slice check */
      {
          int v= show_bits(&s->gb, 16);
          if (get_bits_left(&s->gb) < 16) {
              v >>= 16 - get_bits_left(&s->gb);
          if(v==0)
              return SLICE_END;
      return SLICE_OK;