aribitcoder.h

经过项目量产验证的代码.开发环境是sparc+vxworks. 这个LZMA是专门为sparc做的优化压缩,性能是最好的.

// Compression/AriBitCoder.h


#ifndef __COMPRESSION_BITCODER_H
#define __COMPRESSION_BITCODER_H

#include "Types.h"
#include "RangeCoder.h"

const int kNumBitModelTotalBits  = 11;
const UINT16 kBitModelTotal = (1 << kNumBitModelTotalBits);

/////////////////////////////
// CBitModel

const int kNumMoveBits = 5;

class CBitModel
{
public:
  UINT32 m_Probability;
  void UpdateModel(UINT32 symbol)
  {
    /*
    m_Probability -= (m_Probability + ((symbol - 1) & ((1 << numMoveBits) - 1))) >> numMoveBits;
    m_Probability += (1 - symbol) << (kNumBitModelTotalBits - numMoveBits);
    */
    if (symbol == 0)
      m_Probability += (kBitModelTotal - m_Probability) >> kNumMoveBits;
    else
      m_Probability -= (m_Probability) >> kNumMoveBits;
  }
public:
  void Init() { m_Probability = kBitModelTotal / 2; }
};

class CBitDecoder: public CBitModel
{
public:
  UINT32 Decode(CRangeDecoder *rangeDecoder)
  {
    UINT32 newBound = (rangeDecoder->m_Range >> kNumBitModelTotalBits) * m_Probability;
    if (rangeDecoder->m_Code < newBound)
    {
      rangeDecoder->m_Range = newBound;
      m_Probability += (kBitModelTotal - m_Probability) >> kNumMoveBits;
      if (rangeDecoder->m_Range < kTopValue)
      {
        rangeDecoder->m_Code = (rangeDecoder->m_Code << 8) | rangeDecoder->m_Stream.ReadByte();
        rangeDecoder->m_Range <<= 8;
      }
      return 0;
    }
    else
    {
      rangeDecoder->m_Range -= newBound;
      rangeDecoder->m_Code -= newBound;
      m_Probability -= (m_Probability) >> kNumMoveBits;
      if (rangeDecoder->m_Range < kTopValue)
      {
        rangeDecoder->m_Code = (rangeDecoder->m_Code << 8) | rangeDecoder->m_Stream.ReadByte();
        rangeDecoder->m_Range <<= 8;
      }
      return 1;
    }
  }
};


#endif