146 lines
4.9 KiB
C#
146 lines
4.9 KiB
C#
/* This file is part of SevenZipSharp.
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SevenZipSharp is free software: you can redistribute it and/or modify
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it under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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SevenZipSharp is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with SevenZipSharp. If not, see <http://www.gnu.org/licenses/>.
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*/
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using System;
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namespace SevenZip.Sdk.Compression.RangeCoder
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{
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internal struct BitEncoder
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{
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public const uint kBitModelTotal = (1 << kNumBitModelTotalBits);
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public const int kNumBitModelTotalBits = 11;
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public const int kNumBitPriceShiftBits = 6;
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private const int kNumMoveBits = 5;
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private const int kNumMoveReducingBits = 2;
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private static readonly UInt32[] ProbPrices = new UInt32[kBitModelTotal >> kNumMoveReducingBits];
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private uint Prob;
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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 void Init()
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{
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Prob = kBitModelTotal >> 1;
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}
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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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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()
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{
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return ProbPrices[Prob >> kNumMoveReducingBits];
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}
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public uint GetPrice1()
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{
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return ProbPrices[(kBitModelTotal - Prob) >> kNumMoveReducingBits];
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}
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}
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internal struct BitDecoder
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{
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public const uint kBitModelTotal = (1 << kNumBitModelTotalBits);
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public const int kNumBitModelTotalBits = 11;
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private const int kNumMoveBits = 5;
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private 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()
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{
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Prob = kBitModelTotal >> 1;
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}
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public uint Decode(Decoder rangeDecoder)
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{
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uint newBound = (rangeDecoder.Range >> kNumBitModelTotalBits)*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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} |