134 lines
4.3 KiB
C#
134 lines
4.3 KiB
C#
//
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// Copyright (c) 2008-2011, Kenneth Bell
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//
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// Permission is hereby granted, free of charge, to any person obtaining a
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// copy of this software and associated documentation files (the "Software"),
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// to deal in the Software without restriction, including without limitation
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// the rights to use, copy, modify, merge, publish, distribute, sublicense,
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// and/or sell copies of the Software, and to permit persons to whom the
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// Software is furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in
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// all copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
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// DEALINGS IN THE SOFTWARE.
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//
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//
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// Based on "libbzip2", Copyright (C) 1996-2007 Julian R Seward.
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//
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using System.IO;
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namespace DiscUtils.Compression
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{
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/// <summary>
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/// Represents scheme used by BZip2 where multiple Huffman trees are used as a
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/// virtual Huffman tree, with a logical selector every 50 bits in the bit stream.
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/// </summary>
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internal class BZip2CombinedHuffmanTrees
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{
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private HuffmanTree _activeTree;
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private readonly BitStream _bitstream;
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private int _nextSelector;
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private byte[] _selectors;
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private int _symbolsToNextSelector;
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private HuffmanTree[] _trees;
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public BZip2CombinedHuffmanTrees(BitStream bitstream, int maxSymbols)
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{
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_bitstream = bitstream;
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Initialize(maxSymbols);
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}
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public uint NextSymbol()
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{
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if (_symbolsToNextSelector == 0)
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{
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_symbolsToNextSelector = 50;
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_activeTree = _trees[_selectors[_nextSelector]];
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_nextSelector++;
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}
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_symbolsToNextSelector--;
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return _activeTree.NextSymbol(_bitstream);
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}
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private void Initialize(int maxSymbols)
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{
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int numTrees = (int)_bitstream.Read(3);
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if (numTrees < 2 || numTrees > 6)
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{
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throw new InvalidDataException("Invalid number of tables");
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}
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int numSelectors = (int)_bitstream.Read(15);
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if (numSelectors < 1)
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{
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throw new InvalidDataException("Invalid number of selectors");
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}
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_selectors = new byte[numSelectors];
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MoveToFront mtf = new MoveToFront(numTrees, true);
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for (int i = 0; i < numSelectors; ++i)
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{
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_selectors[i] = mtf.GetAndMove(CountSetBits(numTrees));
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}
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_trees = new HuffmanTree[numTrees];
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for (int t = 0; t < numTrees; ++t)
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{
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uint[] lengths = new uint[maxSymbols];
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uint len = _bitstream.Read(5);
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for (int i = 0; i < maxSymbols; ++i)
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{
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if (len < 1 || len > 20)
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{
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throw new InvalidDataException("Invalid length constructing Huffman tree");
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}
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while (_bitstream.Read(1) != 0)
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{
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len = _bitstream.Read(1) == 0 ? len + 1 : len - 1;
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if (len < 1 || len > 20)
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{
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throw new InvalidDataException("Invalid length constructing Huffman tree");
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}
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}
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lengths[i] = len;
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}
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_trees[t] = new HuffmanTree(lengths);
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}
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_symbolsToNextSelector = 0;
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_nextSelector = 0;
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}
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private byte CountSetBits(int max)
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{
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byte val = 0;
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while (_bitstream.Read(1) != 0)
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{
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val++;
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if (val >= max)
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{
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throw new InvalidDataException("Exceeded max number of consecutive bits");
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}
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}
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return val;
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}
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}
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} |