cabac.c

本源码是H.26L标准的Visual C++源代码

 * \brief
 *    This function is used to arithmetically decode the delta qp
 *     of a given MB.
 ************************************************************************
 */
void readDquantFromBuffer_CABAC(SyntaxElement *se,
                                struct inp_par *inp,
                                struct img_par *img,
                                DecodingEnvironmentPtr dep_dp)
{
  MotionInfoContexts *ctx = img->currentSlice->mot_ctx;
  Macroblock *currMB = &img->mb_data[img->current_mb_nr];

  int act_ctx;
  int act_sym;
  int dquant;

  if (currMB->mb_available[1][0] == NULL)
    act_ctx = 0;
  else
    act_ctx = ( ((currMB->mb_available[1][0])->delta_quant != 0) ? 1 : 0);

  act_sym = biari_decode_symbol(dep_dp,ctx->delta_qp_contexts + act_ctx );
  if (act_sym != 0)
  {
    act_ctx = 2;
    act_sym = unary_bin_decode(dep_dp,ctx->delta_qp_contexts+act_ctx,1);
    act_sym++;
  }

  dquant = (act_sym+1)/2;
  if((act_sym & 0x01)==0)                           // lsb is signed bit
    dquant = -dquant;
  se->value1 = dquant;

#if TRACE
  fprintf(p_trace, "@%d%s\t\t\t%d\n",symbolCount++, se->tracestring, se->value1);
  fflush(p_trace);
#endif
}

/*!
 ************************************************************************
 * \brief
 *    This function is used to arithmetically decode the coded
 *    block pattern of a given MB.
 ************************************************************************
 */
void readCBPFromBuffer_CABAC(SyntaxElement *se,
                             struct inp_par *inp,
                             struct img_par *img,
                             DecodingEnvironmentPtr dep_dp)
{
  TextureInfoContexts *ctx = img->currentSlice->tex_ctx;
  Macroblock *currMB = &img->mb_data[img->current_mb_nr];

  int mb_x, mb_y;
  int a, b;
  int curr_cbp_ctx, curr_cbp_idx;
  int cbp = 0;
  int cbp_bit;
    int mask;

  if ( se->type == SE_CBP_INTRA )
    curr_cbp_idx = 0;
  else
    curr_cbp_idx = 1;

  //  coding of luma part (bit by bit)
  for (mb_y=0; mb_y < 4; mb_y += 2)
  {
    for (mb_x=0; mb_x < 4; mb_x += 2)
    {

      if (mb_y == 0)
      {
        if (currMB->mb_available[0][1] == NULL)
          b = 0;
        else
          b = (( ((currMB->mb_available[0][1])->cbp & (1<<(2+mb_x/2))) == 0) ? 1 : 0);
      }
      else
        b = ( ((cbp & (1<<(mb_x/2))) == 0) ? 1: 0);

      if (mb_x == 0)
      {
        if (currMB->mb_available[1][0] == NULL)
          a = 0;
        else
          a = (( ((currMB->mb_available[1][0])->cbp & (1<<(mb_y+1))) == 0) ? 1 : 0);
      }
      else
        a = ( ((cbp & (1<<mb_y)) == 0) ? 1: 0);

      curr_cbp_ctx = a+2*b;
      mask = (1<<(mb_y+mb_x/2));
            cbp_bit = biari_decode_symbol(dep_dp, ctx->cbp_contexts[curr_cbp_idx][0] + curr_cbp_ctx );
            if (cbp_bit) cbp += mask;
    }
  }

  // coding of chroma part
  b = 0;
  if (currMB->mb_available[0][1] != NULL)
    b = ((currMB->mb_available[0][1])->cbp > 15) ? 1 : 0;

  a = 0;
  if (currMB->mb_available[1][0] != NULL)
    a = ((currMB->mb_available[1][0])->cbp > 15) ? 1 : 0;

  curr_cbp_ctx = a+2*b;
  cbp_bit = biari_decode_symbol(dep_dp, ctx->cbp_contexts[curr_cbp_idx][1] + curr_cbp_ctx );

  if (cbp_bit) // set the chroma bits
  {
    b = 0;
    if (currMB->mb_available[0][1] != NULL)
      if ((currMB->mb_available[0][1])->cbp > 15)
        b = (( ((currMB->mb_available[0][1])->cbp >> 4) == 2) ? 1 : 0);

    a = 0;
    if (currMB->mb_available[1][0] != NULL)
      if ((currMB->mb_available[1][0])->cbp > 15)
        a = (( ((currMB->mb_available[1][0])->cbp >> 4) == 2) ? 1 : 0);

    curr_cbp_ctx = a+2*b;
    cbp_bit = biari_decode_symbol(dep_dp, ctx->cbp_contexts[curr_cbp_idx][2] + curr_cbp_ctx );
    cbp += (cbp_bit == 1) ? 32 : 16;
  }

  se->value1 = cbp;

#if TRACE
  fprintf(p_trace, "@%d      %s\t\t\t%3d\n",symbolCount++, se->tracestring, se->value1);
  fflush(p_trace);
#endif
}

/*!
 ************************************************************************
 * \brief
 *    This function is used to arithmetically decode level and
 *    run of a given MB.
 ************************************************************************
 */
void readRunLevelFromBuffer_CABAC(SyntaxElement *se,
                                  struct inp_par *inp,
                                  struct img_par *img,
                                  DecodingEnvironmentPtr dep_dp)
{
  int level;
  int run=0;
  const int curr_ctx_idx = se->context;
  int curr_level_ctx;
  int sign_of_level;
  int max_run;

  TextureInfoContexts *ctx = img->currentSlice->tex_ctx;
  // Macroblock *currMB = &img->mb_data[img->current_mb_nr];

  level = unary_level_decode(dep_dp,ctx->level_context[curr_ctx_idx]);

  if (level!=0)
  {
    curr_level_ctx = 3;
    sign_of_level = biari_decode_symbol(dep_dp, ctx->level_context[curr_ctx_idx] + curr_level_ctx );
    if (sign_of_level) level = (-1)*level;
      if (curr_ctx_idx != 0 && curr_ctx_idx != 6 && curr_ctx_idx != 5) // not double scan and not DC-chroma
        run = unary_bin_decode(dep_dp,ctx->run_context[curr_ctx_idx],1);
      else
      {
        max_run =  (curr_ctx_idx == 0) ? 7 : 3;  // if double scan max_run = 7; if DC-chroma max_run = 3;
        run = unary_bin_max_decode(dep_dp,ctx->run_context[curr_ctx_idx],1,max_run);
      }
  }
  se->value1 = level;
  se->value2 = run;


#if TRACE
  fprintf(p_trace, "@%d%s\t\t\t%3d \n",symbolCount++, se->tracestring, se->value1);
  fflush(p_trace);
#endif

}

/*!
 ************************************************************************
 * \brief
 *    arithmetic decoding
 ************************************************************************
 */
int readSyntaxElement_CABAC(SyntaxElement *se, struct img_par *img, struct inp_par *inp, DataPartition *this_dataPart)
{
  int curr_len;
  DecodingEnvironmentPtr dep_dp = &(this_dataPart->de_cabac);

  curr_len = arideco_bits_read(dep_dp);

  // perform the actual decoding by calling the appropriate method
  se->reading(se, inp, img, dep_dp);

  return (se->len = (arideco_bits_read(dep_dp) - curr_len));
}

/*!
 ************************************************************************
 * \brief
 *    get slice and header
 ************************************************************************
 */
int readSliceCABAC(struct img_par *img, struct inp_par *inp)
{
  Slice *currSlice = img->currentSlice;
  Bitstream *currStream = currSlice->partArr[0].bitstream;
  unsigned char *code_buffer = currStream->streamBuffer;
  int *read_len = &(currStream->read_len);
  DecodingEnvironmentPtr dep = &((currSlice->partArr[0]).de_cabac);
  int current_header;
  int BitstreamLengthInBytes;
  int info;
  int BitsUsedByHeader = 0, ByteStartPosition;
  int newframe = 0;   //WYK: Oct. 8, 2001, change the method to find a new frame

  currStream->frame_bitoffset =0;

  memset (code_buffer, 0xff, MAX_CODED_FRAME_SIZE);   // this prevents a buffer full with zeros
  BitstreamLengthInBytes = currStream->bitstream_length = GetOneSliceIntoSourceBitBuffer(img, inp, code_buffer);

  // Here we are ready to interpret the picture and slice headers.  Since
  // SliceHeader() gets the data out of the UVLC's len/info
  // array, we need to convert the start of our slice to such a format.


  if (BitstreamLengthInBytes < 4)
    return EOS;

  // Now we have the bits between the current startcode (inclusive) and the
  // next start code in code_buffer.  Now decode the start codes and the headers
  if (31 != GetVLCSymbol (code_buffer, 0, &info, BitstreamLengthInBytes))
  {
    snprintf (errortext, ET_SIZE, "readSliceCABAC: Panic, expected start code symbol, found wrong len");
    error(errortext, 600);
  }
  currStream->frame_bitoffset +=31;
  BitsUsedByHeader+=SliceHeader(img, inp);

  //WYK: Oct. 8, 2001, change the method to find a new frame
  if(img->tr != img->tr_old)
    newframe = 1;
  else 
    newframe = 0;
  img->tr_old = img->tr;
    
  // if the TR of current slice is not identical to the TR of previous received slice, we have a new frame
  if(newframe)
    current_header = SOP;
  else
    current_header = SOS;

  ByteStartPosition = currStream->frame_bitoffset/8;
  if ((currStream->frame_bitoffset)%8 != 0)
    ByteStartPosition++;
  arideco_start_decoding(dep, code_buffer, ByteStartPosition, read_len);


  currSlice->picture_id = img->tr;
  return current_header;

}

/*!
 ************************************************************************
 * \brief
 *    decoding of unary binarization using one or 2 distinct
 *    models for the first and all remaining bins; no terminating
 *    "0" for max_symbol
 ***********************************************************************
 */
unsigned int unary_bin_max_decode(DecodingEnvironmentPtr dep_dp,
                                  BiContextTypePtr ctx,
                                  int ctx_offset,
                                  unsigned int max_symbol)
{
  unsigned int l;
  unsigned int symbol;
  BiContextTypePtr ictx;

  symbol =  biari_decode_symbol(dep_dp, ctx );

  if (symbol==0)
    return 0;
  else
  {
    symbol=0;
    ictx=ctx+ctx_offset;
    do
    {
      l=biari_decode_symbol(dep_dp, ictx);
      symbol++;
    }
    while( (l!=0) && (symbol<max_symbol-1) );
    if ((l!=0) && (symbol==max_symbol-1))
      symbol++;
    return symbol;
  }

}

/*!
 ************************************************************************
 * \brief
 *    decoding of unary binarization of the absolute value
 *    of a level using 3 distinct models by separating the first,
 *    the second and all remaining bins
 ***********************************************************************
 */
unsigned int unary_level_decode(DecodingEnvironmentPtr dep_dp,
                                BiContextTypePtr ctx)
{
  unsigned int l;
  unsigned int symbol;
  int bin=1;
  BiContextTypePtr ictx=ctx;

  symbol = biari_decode_symbol(dep_dp, ictx );

  if (symbol==0)
    return 0;
  else
  {
    symbol=0;
    ictx++;
    do
    {
      l=biari_decode_symbol(dep_dp, ictx  );
      if ((++bin)==2) ictx++;
      symbol++;
    }
    while (l!=0);
    return symbol;
  }
}

/*!
 ************************************************************************
 * \brief
 *    decoding of unary binarization using one or 2 distinct
 *    models for the first and all remaining bins
 ***********************************************************************
 */
unsigned int unary_bin_decode(DecodingEnvironmentPtr dep_dp,
                              BiContextTypePtr ctx,
                              int ctx_offset)
{
  unsigned int l;
  unsigned int symbol;
  BiContextTypePtr ictx;

  symbol = biari_decode_symbol(dep_dp, ctx );

  if (symbol==0)
    return 0;
  else
  {
    symbol=0;
    ictx=ctx+ctx_offset;
    do
    {
      l=biari_decode_symbol(dep_dp, ictx);
      symbol++;
    }
    while( l!=0 );
    return symbol;
  }
}

/*!
 ************************************************************************
 * \brief
 *    decoding of unary binarization of the absolute value of a
 *    mv component using 4 distinct models by separating the first,
 *    the second, intermediate and all remaining bins
 ***********************************************************************
 */
unsigned int unary_mv_decode(DecodingEnvironmentPtr dep_dp,
                             BiContextTypePtr ctx,
                             unsigned int max_bin)
{
  unsigned int l;
  unsigned int bin=1;
  unsigned int symbol;

  BiContextTypePtr ictx=ctx;

  symbol = biari_decode_symbol(dep_dp, ictx );

  if (symbol==0)
    return 0;
  else
  {
    symbol=0;
    ictx++;
    do
    {
      l=biari_decode_symbol(dep_dp, ictx  );
      if ((++bin)==2) ictx++;
      if (bin==max_bin) ictx++;
      symbol++;
    }
    while (l!=0);
    return symbol;
  }
}

/*!
 ************************************************************************
 * \brief
 *    finding end of a slice in case this is not the end of a frame
 ************************************************************************
 */
int cabac_startcode_follows(struct img_par *img, struct inp_par *inp)
{
  Slice *currSlice = img->currentSlice;
  if (img->current_mb_nr == currSlice->last_mb_nr)
    return TRUE;
  return FALSE;
}