michael@0: // LSBFDecoder.h
michael@0: 
michael@0: #ifndef __STREAM_LSBFDECODER_H
michael@0: #define __STREAM_LSBFDECODER_H
michael@0: 
michael@0: #include "../IStream.h"
michael@0: 
michael@0: namespace NStream {
michael@0: namespace NLSBF {
michael@0: 
michael@0: const int kNumBigValueBits = 8 * 4;
michael@0: 
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: extern Byte kInvertTable[256];
michael@0: // the Least Significant Bit of byte is First
michael@0: 
michael@0: template<class TInByte>
michael@0: class CBaseDecoder
michael@0: {
michael@0: protected:
michael@0:   int m_BitPos;
michael@0:   UInt32 m_Value;
michael@0:   TInByte m_Stream;
michael@0: public:
michael@0:   UInt32 NumExtraBytes;
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:   void Init()
michael@0:   {
michael@0:     m_Stream.Init();
michael@0:     m_BitPos = kNumBigValueBits; 
michael@0:     m_Value = 0;
michael@0:     NumExtraBytes = 0;
michael@0:   }
michael@0:   UInt64 GetProcessedSize() const 
michael@0:     { return m_Stream.GetProcessedSize() - (kNumBigValueBits - m_BitPos) / 8; }
michael@0:   UInt64 GetProcessedBitsSize() const 
michael@0:     { return (m_Stream.GetProcessedSize() << 3) - (kNumBigValueBits - m_BitPos); }
michael@0:   int 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:     {
michael@0:       Byte b;
michael@0:       if (!m_Stream.ReadByte(b))
michael@0:       {
michael@0:         b = 0xFF; // check it
michael@0:         NumExtraBytes++;
michael@0:       }
michael@0:       m_Value = (b << (kNumBigValueBits - m_BitPos)) | m_Value;
michael@0:     }
michael@0:   }
michael@0:   
michael@0:   UInt32 ReadBits(int numBits)
michael@0:   {
michael@0:     Normalize();
michael@0:     UInt32 res = m_Value & ((1 << numBits) - 1);
michael@0:     m_BitPos += numBits;
michael@0:     m_Value >>= numBits;
michael@0:     return res;
michael@0:   }
michael@0: 
michael@0:   bool ExtraBitsWereRead() const
michael@0:   {
michael@0:     if (NumExtraBytes == 0)
michael@0:       return false;
michael@0:     return ((UInt32)(kNumBigValueBits - m_BitPos) < (NumExtraBytes << 3));
michael@0:   }
michael@0: };
michael@0: 
michael@0: template<class TInByte>
michael@0: class CDecoder: public CBaseDecoder<TInByte>
michael@0: {
michael@0:   UInt32 m_NormalValue;
michael@0: 
michael@0: public:
michael@0:   void Init()
michael@0:   {
michael@0:     CBaseDecoder<TInByte>::Init();
michael@0:     m_NormalValue = 0;
michael@0:   }
michael@0: 
michael@0:   void Normalize()
michael@0:   {
michael@0:     for (;this->m_BitPos >= 8; this->m_BitPos -= 8)
michael@0:     {
michael@0:       Byte b;
michael@0:       if (!this->m_Stream.ReadByte(b))
michael@0:       {
michael@0:         b = 0xFF; // check it
michael@0:         this->NumExtraBytes++;
michael@0:       }
michael@0:       m_NormalValue = (b << (kNumBigValueBits - this->m_BitPos)) | m_NormalValue;
michael@0:       this->m_Value = (this->m_Value << 8) | kInvertTable[b];
michael@0:     }
michael@0:   }
michael@0:   
michael@0:   UInt32 GetValue(int numBits)
michael@0:   {
michael@0:     Normalize();
michael@0:     return ((this->m_Value >> (8 - this->m_BitPos)) & kMask) >> (kNumValueBits - numBits);
michael@0:   }
michael@0: 
michael@0:   void MovePos(int numBits)
michael@0:   {
michael@0:     this->m_BitPos += numBits;
michael@0:     m_NormalValue >>= numBits;
michael@0:   }
michael@0:   
michael@0:   UInt32 ReadBits(int numBits)
michael@0:   {
michael@0:     Normalize();
michael@0:     UInt32 res = m_NormalValue & ( (1 << numBits) - 1);
michael@0:     MovePos(numBits);
michael@0:     return res;
michael@0:   }
michael@0: };
michael@0: 
michael@0: }}
michael@0: 
michael@0: #endif