74 lines
1.9 KiB
C
74 lines
1.9 KiB
C
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#ifndef __COMPRESSION_BITCODER_H
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#define __COMPRESSION_BITCODER_H
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#include "rngcoder.h"
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namespace NCompression {
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namespace NArithmetic {
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const int kNumBitModelTotalBits = 11;
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const UINT32 kBitModelTotal = (1 << kNumBitModelTotalBits);
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const int kNumMoveReducingBits = 2;
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/////////////////////////////
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// CBitModel
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template <int aNumMoveBits>
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class CBitModel
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{
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public:
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UINT32 m_Probability;
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void UpdateModel(UINT32 aSymbol)
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{
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/*
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m_Probability -= (m_Probability + ((aSymbol - 1) & ((1 << aNumMoveBits) - 1))) >> aNumMoveBits;
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m_Probability += (1 - aSymbol) << (kNumBitModelTotalBits - aNumMoveBits);
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*/
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if (aSymbol == 0)
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m_Probability += (kBitModelTotal - m_Probability) >> aNumMoveBits;
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else
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m_Probability -= (m_Probability) >> aNumMoveBits;
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}
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public:
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void Init() { m_Probability = kBitModelTotal / 2; }
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};
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template <int aNumMoveBits>
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class CBitDecoder: public CBitModel<aNumMoveBits>
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{
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public:
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UINT32 Decode(CRangeDecoder *aRangeDecoder)
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{
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UINT32 aNewBound = (aRangeDecoder->m_Range >> kNumBitModelTotalBits) * CBitModel<aNumMoveBits>::m_Probability;
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if (aRangeDecoder->m_Code < aNewBound)
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{
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aRangeDecoder->m_Range = aNewBound;
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CBitModel<aNumMoveBits>::m_Probability += (kBitModelTotal - CBitModel<aNumMoveBits>::m_Probability) >> aNumMoveBits;
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if (aRangeDecoder->m_Range < kTopValue)
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{
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aRangeDecoder->m_Code = (aRangeDecoder->m_Code << 8) | aRangeDecoder->m_Stream.ReadByte();
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aRangeDecoder->m_Range <<= 8;
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}
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return 0;
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}
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else
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{
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aRangeDecoder->m_Range -= aNewBound;
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aRangeDecoder->m_Code -= aNewBound;
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CBitModel<aNumMoveBits>::m_Probability -= (CBitModel<aNumMoveBits>::m_Probability) >> aNumMoveBits;
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if (aRangeDecoder->m_Range < kTopValue)
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{
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aRangeDecoder->m_Code = (aRangeDecoder->m_Code << 8) | aRangeDecoder->m_Stream.ReadByte();
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aRangeDecoder->m_Range <<= 8;
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}
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return 1;
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}
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}
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};
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}}
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#endif
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