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