source: SHVCSoftware/branches/SHM-2.1-dev/source/Lib/TLibDecoder/TDecBinCoderCABAC.cpp @ 757

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/** \file     TDecBinCoderCABAC.cpp
    \brief    binary entropy decoder of CABAC
*/

#include "TDecBinCoderCABAC.h"

//! \ingroup TLibDecoder
//! \{

TDecBinCABAC::TDecBinCABAC()
: m_pcTComBitstream( 0 )
{
}

TDecBinCABAC::~TDecBinCABAC()
{
}

Void
TDecBinCABAC::init( TComInputBitstream* pcTComBitstream )
{
  m_pcTComBitstream = pcTComBitstream;
}

Void
TDecBinCABAC::uninit()
{
  m_pcTComBitstream = 0;
}

Void
TDecBinCABAC::start()
{
  assert( m_pcTComBitstream->getNumBitsUntilByteAligned() == 0 );
  m_uiRange    = 510;
  m_bitsNeeded = -8;
  m_uiValue    = (m_pcTComBitstream->readByte() << 8);
  m_uiValue   |= m_pcTComBitstream->readByte();
}

Void
TDecBinCABAC::finish()
{
  UInt lastByte;

  m_pcTComBitstream->peekPreviousByte( lastByte );
  // Check for proper stop/alignment pattern
  assert( ((lastByte << (8 + m_bitsNeeded)) & 0xff) == 0x80 );
}

/**
 - Copy CABAC state.
 .
 \param pcTDecBinIf The source CABAC engine.
 */
Void
TDecBinCABAC::copyState( TDecBinIf* pcTDecBinIf )
{
  TDecBinCABAC* pcTDecBinCABAC = pcTDecBinIf->getTDecBinCABAC();
  m_uiRange   = pcTDecBinCABAC->m_uiRange;
  m_uiValue   = pcTDecBinCABAC->m_uiValue;
  m_bitsNeeded= pcTDecBinCABAC->m_bitsNeeded;
}


Void
TDecBinCABAC::decodeBin( UInt& ruiBin, ContextModel &rcCtxModel )
{
  UInt uiLPS = TComCABACTables::sm_aucLPSTable[ rcCtxModel.getState() ][ ( m_uiRange >> 6 ) - 4 ];
  m_uiRange -= uiLPS;
  UInt scaledRange = m_uiRange << 7;
  
  if( m_uiValue < scaledRange )
  {
    // MPS path
    ruiBin = rcCtxModel.getMps();
    rcCtxModel.updateMPS();
    
    if ( scaledRange >= ( 256 << 7 ) )
    {
      return;
    }
    
    m_uiRange = scaledRange >> 6;
    m_uiValue += m_uiValue;
    
    if ( ++m_bitsNeeded == 0 )
    {
      m_bitsNeeded = -8;
      m_uiValue += m_pcTComBitstream->readByte();      
    }
  }
  else
  {
    // LPS path
    Int numBits = TComCABACTables::sm_aucRenormTable[ uiLPS >> 3 ];
    m_uiValue   = ( m_uiValue - scaledRange ) << numBits;
    m_uiRange   = uiLPS << numBits;
    ruiBin      = 1 - rcCtxModel.getMps();
    rcCtxModel.updateLPS();
    
    m_bitsNeeded += numBits;
    
    if ( m_bitsNeeded >= 0 )
    {
      m_uiValue += m_pcTComBitstream->readByte() << m_bitsNeeded;
      m_bitsNeeded -= 8;
    }
  }
}

Void
TDecBinCABAC::decodeBinEP( UInt& ruiBin )
{
  m_uiValue += m_uiValue;
  
  if ( ++m_bitsNeeded >= 0 )
  {
    m_bitsNeeded = -8;
    m_uiValue += m_pcTComBitstream->readByte();
  }
  
  ruiBin = 0;
  UInt scaledRange = m_uiRange << 7;
  if ( m_uiValue >= scaledRange )
  {
    ruiBin = 1;
    m_uiValue -= scaledRange;
  }
}

Void TDecBinCABAC::decodeBinsEP( UInt& ruiBin, Int numBins )
{
  UInt bins = 0;
  
  while ( numBins > 8 )
  {
    m_uiValue = ( m_uiValue << 8 ) + ( m_pcTComBitstream->readByte() << ( 8 + m_bitsNeeded ) );
    
    UInt scaledRange = m_uiRange << 15;
    for ( Int i = 0; i < 8; i++ )
    {
      bins += bins;
      scaledRange >>= 1;
      if ( m_uiValue >= scaledRange )
      {
        bins++;
        m_uiValue -= scaledRange;
      }
    }
    numBins -= 8;
  }
  
  m_bitsNeeded += numBins;
  m_uiValue <<= numBins;
  
  if ( m_bitsNeeded >= 0 )
  {
    m_uiValue += m_pcTComBitstream->readByte() << m_bitsNeeded;
    m_bitsNeeded -= 8;
  }
  
  UInt scaledRange = m_uiRange << ( numBins + 7 );
  for ( Int i = 0; i < numBins; i++ )
  {
    bins += bins;
    scaledRange >>= 1;
    if ( m_uiValue >= scaledRange )
    {
      bins++;
      m_uiValue -= scaledRange;
    }
  }
  
  ruiBin = bins;
}

Void
TDecBinCABAC::decodeBinTrm( UInt& ruiBin )
{
  m_uiRange -= 2;
  UInt scaledRange = m_uiRange << 7;
  if( m_uiValue >= scaledRange )
  {
    ruiBin = 1;
  }
  else
  {
    ruiBin = 0;
    if ( scaledRange < ( 256 << 7 ) )
    {
      m_uiRange = scaledRange >> 6;
      m_uiValue += m_uiValue;
      
      if ( ++m_bitsNeeded == 0 )
      {
        m_bitsNeeded = -8;
        m_uiValue += m_pcTComBitstream->readByte();      
      }
    }
  }
}

/** Read a PCM code.
 * \param uiLength code bit-depth
 * \param ruiCode pointer to PCM code value
 * \returns Void
 */
Void  TDecBinCABAC::xReadPCMCode(UInt uiLength, UInt& ruiCode)
{
  assert ( uiLength > 0 );
  m_pcTComBitstream->read (uiLength, ruiCode);
}
//! \}