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// BitmDecoder.h -- the Most Significant Bit of byte is First
#ifndef __BITM_DECODER_H
#define __BITM_DECODER_H
#include "../IStream.h"
namespace NBitm {
const unsigned kNumBigValueBits = 8 * 4;
const unsigned kNumValueBytes = 3;
const unsigned kNumValueBits = 8 * kNumValueBytes;
const UInt32 kMask = (1 << kNumValueBits) - 1;
// _bitPos - the number of free bits (high bits in _value)
// (kNumBigValueBits - _bitPos) = (32 - _bitPos) == the number of ready to read bits (low bits of _value)
template<class TInByte>
class CDecoder
{
unsigned _bitPos;
UInt32 _value;
TInByte _stream;
public:
bool Create(UInt32 bufSize) { return _stream.Create(bufSize); }
void SetStream(ISequentialInStream *inStream) { _stream.SetStream(inStream);}
void Init()
{
_stream.Init();
_bitPos = kNumBigValueBits;
_value = 0;
Normalize();
}
UInt64 GetStreamSize() const { return _stream.GetStreamSize(); }
UInt64 GetProcessedSize() const { return _stream.GetProcessedSize() - ((kNumBigValueBits - _bitPos) >> 3); }
bool ExtraBitsWereRead() const
{
return (_stream.NumExtraBytes > 4 || kNumBigValueBits - _bitPos < (_stream.NumExtraBytes << 3));
}
bool ExtraBitsWereRead_Fast() const
{
return (_stream.NumExtraBytes > 4);
}
void Normalize()
{
for (; _bitPos >= 8; _bitPos -= 8)
_value = (_value << 8) | _stream.ReadByte();
}
UInt32 GetValue(unsigned numBits) const
{
// return (_value << _bitPos) >> (kNumBigValueBits - numBits);
return ((_value >> (8 - _bitPos)) & kMask) >> (kNumValueBits - numBits);
}
void MovePos(unsigned numBits)
{
_bitPos += numBits;
Normalize();
}
UInt32 ReadBits(unsigned numBits)
{
UInt32 res = GetValue(numBits);
MovePos(numBits);
return res;
}
void AlignToByte() { MovePos((kNumBigValueBits - _bitPos) & 7); }
};
}
#endif
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