52 lines
1.2 KiB
C#
52 lines
1.2 KiB
C#
using System;
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namespace SevenZip.Compression.RangeCoder
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{
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struct BitDecoder
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{
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public const int kNumBitModelTotalBits = 11;
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public const uint kBitModelTotal = (1 << kNumBitModelTotalBits);
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const int kNumMoveBits = 5;
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uint Prob;
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public void UpdateModel(int numMoveBits, uint symbol)
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{
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if (symbol == 0)
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Prob += (kBitModelTotal - Prob) >> numMoveBits;
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else
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Prob -= (Prob) >> numMoveBits;
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}
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public void Init() { Prob = kBitModelTotal >> 1; }
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public uint Decode(RangeCoder.Decoder rangeDecoder)
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{
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uint newBound = (uint)(rangeDecoder.Range >> kNumBitModelTotalBits) * (uint)Prob;
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if (rangeDecoder.Code < newBound)
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{
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rangeDecoder.Range = newBound;
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Prob += (kBitModelTotal - Prob) >> kNumMoveBits;
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if (rangeDecoder.Range < Decoder.kTopValue)
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{
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rangeDecoder.Code = (rangeDecoder.Code << 8) | (byte)rangeDecoder.Stream.ReadByte();
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rangeDecoder.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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rangeDecoder.Range -= newBound;
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rangeDecoder.Code -= newBound;
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Prob -= (Prob) >> kNumMoveBits;
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if (rangeDecoder.Range < Decoder.kTopValue)
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{
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rangeDecoder.Code = (rangeDecoder.Code << 8) | (byte)rangeDecoder.Stream.ReadByte();
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rangeDecoder.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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