other-licenses/7zstub/src/7zip/Common/MSBFDecoder.h

   1 // MSBFDecoder.h
   2 // the Most Significant Bit of byte is First
   3
   4 #ifndef __STREAM_MSBFDECODER_H
   5 #define __STREAM_MSBFDECODER_H
   6
   7 #include "../../Common/Types.h"
   8 #include "../IStream.h"
   9
  10 namespace NStream {
  11 namespace NMSBF {
  12
  13 const int kNumBigValueBits = 8 * 4;
  14 const int kNumValueBytes = 3;
  15 const int kNumValueBits = 8  * kNumValueBytes;
  16
  17 const UInt32 kMask = (1 << kNumValueBits) - 1;
  18
  19 template<class TInByte>
  20 class CDecoder
  21 {
  22   UInt32 m_BitPos;
  23   UInt32 m_Value;
  24 public:
  25   TInByte m_Stream;
  26   bool Create(UInt32 bufferSize) { return m_Stream.Create(bufferSize); }
  27   void SetStream(ISequentialInStream *inStream) { m_Stream.SetStream(inStream);}
  28   void ReleaseStream() { m_Stream.ReleaseStream();}
  29
  30   void Init()
  31   {
  32     m_Stream.Init();
  33     m_BitPos = kNumBigValueBits;
  34     Normalize();
  35   }
  36
  37   UInt64 GetProcessedSize() const
  38     { return m_Stream.GetProcessedSize() - (kNumBigValueBits - m_BitPos) / 8; }
  39   UInt32 GetBitPosition() const { return (m_BitPos & 7); }
  40
  41   void Normalize()
  42   {
  43     for (;m_BitPos >= 8; m_BitPos -= 8)
  44       m_Value = (m_Value << 8) | m_Stream.ReadByte();
  45   }
  46
  47   UInt32 GetValue(UInt32 numBits) const
  48   {
  49     // return (m_Value << m_BitPos) >> (kNumBigValueBits - numBits);
  50     return ((m_Value >> (8 - m_BitPos)) & kMask) >> (kNumValueBits - numBits);
  51   }
  52
  53   void MovePos(UInt32 numBits)
  54   {
  55     m_BitPos += numBits;
  56     Normalize();
  57   }
  58
  59   UInt32 ReadBits(UInt32 numBits)
  60   {
  61     UInt32 res = GetValue(numBits);
  62     MovePos(numBits);
  63     return res;
  64   }
  65 };
  66
  67 }}
  68
  69 #endif