BinDecoder.cpp

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/** \file     BinDecoder.cpp
 *  \brief    Low level binary symbol writer
 */


#include "BinDecoder.h"
#include "CommonLib/Rom.h"
#if RExt__DECODER_DEBUG_BIT_STATISTICS
#include "CommonLib/CodingStatistics.h"
#endif

#include "CommonLib/dtrace_next.h"

template<class BinProbModel>
BinDecoderBase::BinDecoderBase(const BinProbModel *dummy)
  : Ctx(dummy), m_bitstream(nullptr), m_range(0), m_value(0), m_bitsNeeded(0)
{}

void BinDecoderBase::init( InputBitstream* bitstream )
{
  m_bitstream = bitstream;
}

void BinDecoderBase::uninit()
{
  m_bitstream = nullptr;
}

void BinDecoderBase::start()
{
  CHECK(m_bitstream->getNumBitsUntilByteAligned(), "Bitstream is not byte aligned.");
#if RExt__DECODER_DEBUG_BIT_STATISTICS
  CodingStatistics::UpdateCABACStat(STATS__CABAC_INITIALISATION, 512, 510, 0);
#endif
  m_range       = 510;
  m_value       = (m_bitstream->readByte() << 8) + m_bitstream->readByte();
  m_bitsNeeded  = -8;
}

void BinDecoderBase::finish()
{
  unsigned lastByte;
  m_bitstream->peekPreviousByte(lastByte);
  CHECK( ( ( lastByte << ( 8 + m_bitsNeeded ) ) & 0xff ) != 0x80,
        "No proper stop/alignment pattern at end of CABAC stream." );
}

void BinDecoderBase::reset( int qp, int initId )
{
  Ctx::init( qp, initId );
  start();
}

void BinDecoderBase::riceStatReset(int bitDepth, bool persistentRiceAdaptationEnabledFlag)
{
  Ctx::riceStatReset(bitDepth, persistentRiceAdaptationEnabledFlag);
}

unsigned BinDecoderBase::decodeBinEP()
{
  m_value += m_value;
  if( ++m_bitsNeeded >= 0 )
  {
    m_value += m_bitstream->readByte();
    m_bitsNeeded      = -8;
  }

  unsigned bin = 0;
  unsigned scaledRange = m_range << 7;
  if (m_value >= scaledRange)
  {
    m_value -= scaledRange;
    bin        = 1;
  }
#if RExt__DECODER_DEBUG_BIT_STATISTICS
  CodingStatistics::IncrementStatisticEP( *ptype, 1, int(bin) );
#endif
  DTRACE(g_trace_ctx, D_CABAC, "%d  %d  EP=%d \n", DTRACE_GET_COUNTER(g_trace_ctx, D_CABAC), m_range, bin);
  return bin;
}

unsigned BinDecoderBase::decodeBinsEP( unsigned numBins )
{
#if ENABLE_TRACING
  int numBinsOrig = numBins;
#endif

  if (m_range == 256)
  {
    return decodeAlignedBinsEP( numBins );
  }
  unsigned remBins = numBins;
  unsigned bins    = 0;
  while(   remBins > 8 )
  {
    m_value              = (m_value << 8) + (m_bitstream->readByte() << (8 + m_bitsNeeded));
    unsigned scaledRange = m_range << 15;
    for( int i = 0; i < 8; i++ )
    {
      bins += bins;
      scaledRange >>= 1;
      if (m_value >= scaledRange)
      {
        bins    ++;
        m_value -= scaledRange;
      }
    }
    remBins -= 8;
  }
  m_bitsNeeded   += remBins;
  m_value <<= remBins;
  if( m_bitsNeeded >= 0 )
  {
    m_value += m_bitstream->readByte() << m_bitsNeeded;
    m_bitsNeeded -= 8;
  }
  unsigned scaledRange = m_range << (remBins + 7);
  for ( int i = 0; i < remBins; i++ )
  {
    bins += bins;
    scaledRange >>= 1;
    if (m_value >= scaledRange)
    {
      bins    ++;
      m_value -= scaledRange;
    }
  }
#if RExt__DECODER_DEBUG_BIT_STATISTICS
  CodingStatistics::IncrementStatisticEP( *ptype, numBins, int(bins) );
#endif
#if ENABLE_TRACING
  for( int i = 0; i < numBinsOrig; i++ )
  {
    DTRACE(g_trace_ctx, D_CABAC, "%d  %d  EP=%d \n", DTRACE_GET_COUNTER(g_trace_ctx, D_CABAC), m_range,
           (bins >> (numBinsOrig - 1 - i)) & 1);
  }
#endif
  return bins;
}

unsigned BinDecoderBase::decodeRemAbsEP(unsigned goRicePar, unsigned cutoff, int maxLog2TrDynamicRange)
{
  unsigned prefix = 0;
  {
    const unsigned  maxPrefix = 32 - maxLog2TrDynamicRange;
    unsigned        codeWord = 0;
    do
    {
      prefix++;
      codeWord = decodeBinEP();
    } while (codeWord && prefix < maxPrefix);
    prefix -= 1 - codeWord;
  }

  unsigned length = goRicePar, offset;
  if (prefix < cutoff)
  {
    offset = prefix << goRicePar;
  }
  else
  {
    offset = (((1 << (prefix - cutoff)) + cutoff - 1) << goRicePar);
    {
      length += (prefix == (32 - maxLog2TrDynamicRange) ? maxLog2TrDynamicRange - goRicePar : prefix - cutoff);
    }
  }
  return offset + decodeBinsEP(length);
}

unsigned BinDecoderBase::decodeBinTrm()
{
  m_range -= 2;
  unsigned scaledRange = m_range << 7;
  if (m_value >= scaledRange)
  {
#if RExt__DECODER_DEBUG_BIT_STATISTICS
    CodingStatistics::UpdateCABACStat(STATS__CABAC_TRM_BITS, m_range + 2, 2, 1);
    CodingStatistics::IncrementStatisticEP( STATS__BYTE_ALIGNMENT_BITS, -m_bitsNeeded, 0 );
#endif
    return 1;
  }
  else
  {
#if RExt__DECODER_DEBUG_BIT_STATISTICS
    CodingStatistics::UpdateCABACStat(STATS__CABAC_TRM_BITS, m_range + 2, m_range, 0);
#endif
    if (m_range < 256)
    {
      m_range += m_range;
      m_value += m_value;
      if( ++m_bitsNeeded == 0 )
      {
        m_value += m_bitstream->readByte();
        m_bitsNeeded  = -8;
      }
    }
    return 0;
  }
}

void BinDecoderBase::align()
{
#if RExt__DECODER_DEBUG_BIT_STATISTICS
  CodingStatistics::UpdateCABACStat(STATS__CABAC_EP_BIT_ALIGNMENT, m_range, 256, 0);
#endif
  m_range = 256;
}

unsigned BinDecoderBase::decodeAlignedBinsEP( unsigned numBins )
{
#if ENABLE_TRACING
  int numBinsOrig = numBins;
#endif
  unsigned remBins = numBins;
  unsigned bins    = 0;
  while(   remBins > 0 )
  {
    // The MSB of m_value is known to be 0 because range is 256. Therefore:
    //   > The comparison against the symbol range of 128 is simply a test on the next-most-significant bit
    //   > "Subtracting" the symbol range if the decoded bin is 1 simply involves clearing that bit.
    //  As a result, the required bins are simply the <binsToRead> next-most-significant bits of m_value
    //  (m_value is stored MSB-aligned in a 16-bit buffer - hence the shift of 15)
    //
    //    m_value = |0|V|V|V|V|V|V|V|V|B|B|B|B|B|B|B|
    //    (V = usable bit, B = potential buffered bit (buffer refills when m_bitsNeeded >= 0))
    //
    unsigned binsToRead = std::min<unsigned>( remBins, 8 ); //read bytes if able to take advantage of the system's byte-read function
    unsigned binMask    = ( 1 << binsToRead ) - 1;
    unsigned newBins    = (m_value >> (15 - binsToRead)) & binMask;
    bins                = ( bins    << binsToRead) | newBins;
    m_value             = (m_value << binsToRead) & 0x7FFF;
    remBins            -= binsToRead;
    m_bitsNeeded       += binsToRead;
    if( m_bitsNeeded >= 0 )
    {
      m_value |= m_bitstream->readByte() << m_bitsNeeded;
      m_bitsNeeded     -= 8;
    }
  }
#if RExt__DECODER_DEBUG_BIT_STATISTICS
  CodingStatistics::IncrementStatisticEP( *ptype, numBins, int(bins) );
#endif
#if ENABLE_TRACING
  for( int i = 0; i < numBinsOrig; i++ )
  {
    DTRACE(g_trace_ctx, D_CABAC, "%d  %d  EP=%d \n", DTRACE_GET_COUNTER(g_trace_ctx, D_CABAC), m_range,
           (bins >> (numBinsOrig - 1 - i)) & 1);
  }
#endif
  return bins;
}

template<class BinProbModel>
TBinDecoder<BinProbModel>::TBinDecoder()
  : BinDecoderBase(static_cast<const BinProbModel *>(nullptr)), m_ctx(static_cast<CtxStore<BinProbModel> &>(*this))
{}

template <class BinProbModel>
unsigned TBinDecoder<BinProbModel>::decodeBin( unsigned ctxId )
{
  BinProbModel &probModel = m_ctx[ctxId];
  unsigned      bin       = probModel.mps();
  uint32_t      lpsRange  = probModel.getLPS(m_range);

  DTRACE(g_trace_ctx, D_CABAC, "%d %d %d  [%d:%d]  %2d(MPS=%d)  ", DTRACE_GET_COUNTER(g_trace_ctx, D_CABAC), ctxId,
         m_range, m_range - lpsRange, lpsRange, (unsigned int) (probModel.state()),
         m_value < ((m_range - lpsRange) << 7));

  m_range -= lpsRange;
  uint32_t scaledRange = m_range << 7;
  if (m_value < scaledRange)
  {
#if RExt__DECODER_DEBUG_BIT_STATISTICS
    CodingStatistics::UpdateCABACStat(*ptype, m_range + lpsRange, m_range, int(bin));
#endif
    // MPS path
    if (m_range < 256)
    {
      int numBits = probModel.getRenormBitsRange(m_range);
      m_range <<= numBits;
      m_value <<= numBits;
      m_bitsNeeded += numBits;
      if( m_bitsNeeded >= 0 )
      {
        m_value += m_bitstream->readByte() << m_bitsNeeded;
        m_bitsNeeded -= 8;
      }
    }
  }
  else
  {
    bin = 1 - bin;
#if RExt__DECODER_DEBUG_BIT_STATISTICS
    CodingStatistics::UpdateCABACStat(*ptype, m_range + lpsRange, lpsRange, int(bin));
#endif
    // LPS path
    int numBits = probModel.getRenormBitsLPS(lpsRange);
    m_value -= scaledRange;
    m_value = m_value << numBits;
    m_range = lpsRange << numBits;
    m_bitsNeeded += numBits;
    if( m_bitsNeeded >= 0 )
    {
      m_value += m_bitstream->readByte() << m_bitsNeeded;
      m_bitsNeeded -= 8;
    }
  }
  probModel.update(bin);
  //DTRACE_DECR_COUNTER( g_trace_ctx, D_CABAC );
  DTRACE_WITHOUT_COUNT( g_trace_ctx, D_CABAC, "  -  " "%d" "\n", bin );
  return  bin;
}

template class TBinDecoder<BinProbModel_Std>;