Mercurial > vba-linux

     1 // BitmDecoder.h -- the Most Significant Bit of byte is First

     2 

     3 #ifndef __BITM_DECODER_H

     4 #define __BITM_DECODER_H

     5 

     6 #include "../IStream.h"

     7 

     8 namespace NBitm {

     9 

    10 const int kNumBigValueBits = 8 * 4;

    11 const int kNumValueBytes = 3;

    12 const int kNumValueBits = 8  * kNumValueBytes;

    13 

    14 const UInt32 kMask = (1 << kNumValueBits) - 1;

    15 

    16 template<class TInByte>

    17 class CDecoder

    18 {

    19   UInt32 m_BitPos;

    20   UInt32 m_Value;

    21 public:

    22   TInByte m_Stream;

    23   bool Create(UInt32 bufferSize) { return m_Stream.Create(bufferSize); }

    24   void SetStream(ISequentialInStream *inStream) { m_Stream.SetStream(inStream);}

    25   void ReleaseStream() { m_Stream.ReleaseStream();}

    26 

    27   void Init()

    28   {

    29     m_Stream.Init();

    30     m_BitPos = kNumBigValueBits;

    31     Normalize();

    32   }

    33   

    34   UInt64 GetProcessedSize() const

    35     { return m_Stream.GetProcessedSize() - (kNumBigValueBits - m_BitPos) / 8; }

    36   UInt32 GetBitPosition() const { return (m_BitPos & 7); }

    37   

    38   void Normalize()

    39   {

    40     for (;m_BitPos >= 8; m_BitPos -= 8)

    41       m_Value = (m_Value << 8) | m_Stream.ReadByte();

    42   }

    43 

    44   UInt32 GetValue(UInt32 numBits) const

    45   {

    46     // return (m_Value << m_BitPos) >> (kNumBigValueBits - numBits);

    47     return ((m_Value >> (8 - m_BitPos)) & kMask) >> (kNumValueBits - numBits);

    48   }

    49   

    50   void MovePos(UInt32 numBits)

    51   {

    52     m_BitPos += numBits;

    53     Normalize();

    54   }

    55   

    56   UInt32 ReadBits(UInt32 numBits)

    57   {

    58     UInt32 res = GetValue(numBits);

    59     MovePos(numBits);

    60     return res;

    61   }

    62 };

    63 

    64 }

    65 

    66 #endif
author	Robert McIntyre <rlm@mit.edu>
date	Sat, 03 Mar 2012 10:31:27 -0600
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