rngcoder.h

SFC游戏模拟器 snes9x 1.43 的原代码

/*
Copyright (C) 2002 Andrea Mazzoleni ( http://advancemame.sf.net )
Copyright (C) 2001-4 Igor Pavlov ( http://www.7-zip.org )

This library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.

This library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/

#ifndef __COMPRESSION_RANGECODER_H
#define __COMPRESSION_RANGECODER_H

#include "inbyte.h"

namespace NCompression {
namespace NArithmetic {

const UINT32 kNumTopBits = 24;
const UINT32 kTopValue = (1 << kNumTopBits);

class CRangeDecoder
{
public:
  NStream::CInByte m_Stream;
  UINT32 m_Range;
  UINT32 m_Code;
  UINT32 m_Word;
  void Normalize()
  {
    while (m_Range < kTopValue)
    {
      m_Code = (m_Code << 8) | m_Stream.ReadByte();
      m_Range <<= 8;
    }
  }
  
  void Init(ISequentialInStream *aStream)
  {
    m_Stream.Init(aStream);
    m_Code = 0;
    m_Range = UINT32(-1);
    for(int i = 0; i < 5; i++)
      m_Code = (m_Code << 8) | m_Stream.ReadByte();
  }

  UINT32 GetThreshold(UINT32 aTotal)
  {
    return (m_Code) / ( m_Range /= aTotal);
  }

  void Decode(UINT32 aStart, UINT32 aSize, UINT32 aTotal)
  {
    m_Code -= aStart * m_Range;
    m_Range *= aSize;
    Normalize();
  }

  /*
  UINT32 DecodeDirectBitsDiv(UINT32 aNumTotalBits)
  {
    m_Range >>= aNumTotalBits;
    UINT32 aThreshold = m_Code / m_Range;
    m_Code -= aThreshold * m_Range;
    
    Normalize();
    return aThreshold;
  }

  UINT32 DecodeDirectBitsDiv2(UINT32 aNumTotalBits)
  {
    if (aNumTotalBits <= kNumBottomBits)
      return DecodeDirectBitsDiv(aNumTotalBits);
    UINT32 aResult = DecodeDirectBitsDiv(aNumTotalBits - kNumBottomBits) << kNumBottomBits;
    return (aResult | DecodeDirectBitsDiv(kNumBottomBits));
  }
  */

  UINT32 DecodeDirectBits(UINT32 aNumTotalBits)
  {
    UINT32 aRange = m_Range;
    UINT32 aCode = m_Code;        
    UINT32 aResult = 0;
    for (UINT32 i = aNumTotalBits; i > 0; i--)
    {
      aRange >>= 1;
      /*
      aResult <<= 1;
      if (aCode >= aRange)
      {
        aCode -= aRange;
        aResult |= 1;
      }
      */
      UINT32 t = (aCode - aRange) >> 31;
      aCode -= aRange & (t - 1);
      // aRange = aRangeTmp + ((aRange & 1) & (1 - t));
      aResult = (aResult << 1) | (1 - t);

      if (aRange < kTopValue)
      {
        aCode = (aCode << 8) | m_Stream.ReadByte();
        aRange <<= 8; 
      }
    }
    m_Range = aRange;
    m_Code = aCode;
    return aResult;
  }

  UINT32 DecodeBit(UINT32 aSize0, UINT32 aNumTotalBits)
  {
    UINT32 aNewBound = (m_Range >> aNumTotalBits) * aSize0;
    UINT32 aSymbol;
    if (m_Code < aNewBound)
    {
      aSymbol = 0;
      m_Range = aNewBound;
    }
    else
    {
      aSymbol = 1;
      m_Code -= aNewBound;
      m_Range -= aNewBound;
    }
    Normalize();
    return aSymbol;
  }

  UINT64 GetProcessedSize() {return m_Stream.GetProcessedSize(); }
};

}}

#endif