michael@0: // MSBFDecoder.h
michael@0: // the Most Significant Bit of byte is First
michael@0: 
michael@0: #ifndef __STREAM_MSBFDECODER_H
michael@0: #define __STREAM_MSBFDECODER_H
michael@0: 
michael@0: #include "../../Common/Types.h"
michael@0: #include "../IStream.h"
michael@0: 
michael@0: namespace NStream {
michael@0: namespace NMSBF {
michael@0: 
michael@0: const int kNumBigValueBits = 8 * 4;
michael@0: const int kNumValueBytes = 3;
michael@0: const int kNumValueBits = 8  * kNumValueBytes;
michael@0: 
michael@0: const UInt32 kMask = (1 << kNumValueBits) - 1;
michael@0: 
michael@0: template<class TInByte>
michael@0: class CDecoder
michael@0: {
michael@0:   UInt32 m_BitPos;
michael@0:   UInt32 m_Value;
michael@0: public:
michael@0:   TInByte m_Stream;
michael@0:   bool Create(UInt32 bufferSize) { return m_Stream.Create(bufferSize); }
michael@0:   void SetStream(ISequentialInStream *inStream) { m_Stream.SetStream(inStream);}
michael@0:   void ReleaseStream() { m_Stream.ReleaseStream();}
michael@0: 
michael@0:   void Init()
michael@0:   {
michael@0:     m_Stream.Init();
michael@0:     m_BitPos = kNumBigValueBits; 
michael@0:     Normalize();
michael@0:   }
michael@0:   
michael@0:   UInt64 GetProcessedSize() const 
michael@0:     { return m_Stream.GetProcessedSize() - (kNumBigValueBits - m_BitPos) / 8; }
michael@0:   UInt32 GetBitPosition() const { return (m_BitPos & 7); }
michael@0:   
michael@0:   void Normalize()
michael@0:   {
michael@0:     for (;m_BitPos >= 8; m_BitPos -= 8)
michael@0:       m_Value = (m_Value << 8) | m_Stream.ReadByte();
michael@0:   }
michael@0: 
michael@0:   UInt32 GetValue(UInt32 numBits) const
michael@0:   {
michael@0:     // return (m_Value << m_BitPos) >> (kNumBigValueBits - numBits);
michael@0:     return ((m_Value >> (8 - m_BitPos)) & kMask) >> (kNumValueBits - numBits);
michael@0:   }
michael@0:   
michael@0:   void MovePos(UInt32 numBits)
michael@0:   {
michael@0:     m_BitPos += numBits;
michael@0:     Normalize();
michael@0:   }
michael@0:   
michael@0:   UInt32 ReadBits(UInt32 numBits)
michael@0:   {
michael@0:     UInt32 res = GetValue(numBits);
michael@0:     MovePos(numBits);
michael@0:     return res;
michael@0:   }
michael@0: };
michael@0: 
michael@0: }}
michael@0: 
michael@0: #endif