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118 lines
3.2 KiB
118 lines
3.2 KiB
using System;
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namespace SevenZip.Compression.RangeCoder
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{
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struct BitEncoder
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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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const int kNumMoveReducingBits = 2;
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public const int kNumBitPriceShiftBits = 6;
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uint Prob;
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public void Init() { Prob = kBitModelTotal >> 1; }
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public void UpdateModel(uint symbol)
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{
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if (symbol == 0)
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Prob += (kBitModelTotal - Prob) >> kNumMoveBits;
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else
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Prob -= (Prob) >> kNumMoveBits;
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}
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public void Encode(Encoder encoder, uint symbol)
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{
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// encoder.EncodeBit(Prob, kNumBitModelTotalBits, symbol);
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// UpdateModel(symbol);
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uint newBound = (encoder.Range >> kNumBitModelTotalBits) * Prob;
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if (symbol == 0)
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{
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encoder.Range = newBound;
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Prob += (kBitModelTotal - Prob) >> kNumMoveBits;
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}
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else
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{
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encoder.Low += newBound;
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encoder.Range -= newBound;
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Prob -= (Prob) >> kNumMoveBits;
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}
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if (encoder.Range < Encoder.kTopValue)
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{
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encoder.Range <<= 8;
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encoder.ShiftLow();
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}
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}
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private static UInt32[] ProbPrices = new UInt32[kBitModelTotal >> kNumMoveReducingBits];
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static BitEncoder()
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{
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const int kNumBits = (kNumBitModelTotalBits - kNumMoveReducingBits);
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for (int i = kNumBits - 1; i >= 0; i--)
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{
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UInt32 start = (UInt32)1 << (kNumBits - i - 1);
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UInt32 end = (UInt32)1 << (kNumBits - i);
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for (UInt32 j = start; j < end; j++)
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ProbPrices[j] = ((UInt32)i << kNumBitPriceShiftBits) +
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(((end - j) << kNumBitPriceShiftBits) >> (kNumBits - i - 1));
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}
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}
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public uint GetPrice(uint symbol)
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{
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return ProbPrices[(((Prob - symbol) ^ ((-(int)symbol))) & (kBitModelTotal - 1)) >> kNumMoveReducingBits];
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}
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public uint GetPrice0() { return ProbPrices[Prob >> kNumMoveReducingBits]; }
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public uint GetPrice1() { return ProbPrices[(kBitModelTotal - Prob) >> kNumMoveReducingBits]; }
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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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