152 lines
5.0 KiB
C#
152 lines
5.0 KiB
C#
using ICSharpCode.SharpZipLib.Zip.Compression.Streams;
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using System;
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using System.Collections.Generic;
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namespace ICSharpCode.SharpZipLib.Zip.Compression
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{
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internal class InflaterDynHeader
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{
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#region Constants
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// maximum number of literal/length codes
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private const int LITLEN_MAX = 286;
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// maximum number of distance codes
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private const int DIST_MAX = 30;
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// maximum data code lengths to read
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private const int CODELEN_MAX = LITLEN_MAX + DIST_MAX;
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// maximum meta code length codes to read
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private const int META_MAX = 19;
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private static readonly int[] MetaCodeLengthIndex =
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{ 16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15 };
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#endregion Constants
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/// <summary>
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/// Continue decoding header from <see cref="input"/> until more bits are needed or decoding has been completed
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/// </summary>
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/// <returns>Returns whether decoding could be completed</returns>
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public bool AttemptRead()
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=> !state.MoveNext() || state.Current;
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public InflaterDynHeader(StreamManipulator input)
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{
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this.input = input;
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stateMachine = CreateStateMachine();
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state = stateMachine.GetEnumerator();
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}
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private IEnumerable<bool> CreateStateMachine()
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{
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// Read initial code length counts from header
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while (!input.TryGetBits(5, ref litLenCodeCount, 257)) yield return false;
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while (!input.TryGetBits(5, ref distanceCodeCount, 1)) yield return false;
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while (!input.TryGetBits(4, ref metaCodeCount, 4)) yield return false;
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var dataCodeCount = litLenCodeCount + distanceCodeCount;
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if (litLenCodeCount > LITLEN_MAX) throw new ValueOutOfRangeException(nameof(litLenCodeCount));
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if (distanceCodeCount > DIST_MAX) throw new ValueOutOfRangeException(nameof(distanceCodeCount));
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if (metaCodeCount > META_MAX) throw new ValueOutOfRangeException(nameof(metaCodeCount));
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// Load code lengths for the meta tree from the header bits
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for (int i = 0; i < metaCodeCount; i++)
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{
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while (!input.TryGetBits(3, ref codeLengths, MetaCodeLengthIndex[i])) yield return false;
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}
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var metaCodeTree = new InflaterHuffmanTree(codeLengths);
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// Decompress the meta tree symbols into the data table code lengths
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int index = 0;
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while (index < dataCodeCount)
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{
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byte codeLength;
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int symbol;
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while ((symbol = metaCodeTree.GetSymbol(input)) < 0) yield return false;
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if (symbol < 16)
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{
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// append literal code length
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codeLengths[index++] = (byte)symbol;
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}
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else
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{
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int repeatCount = 0;
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if (symbol == 16) // Repeat last code length 3..6 times
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{
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if (index == 0)
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throw new StreamDecodingException("Cannot repeat previous code length when no other code length has been read");
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codeLength = codeLengths[index - 1];
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// 2 bits + 3, [3..6]
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while (!input.TryGetBits(2, ref repeatCount, 3)) yield return false;
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}
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else if (symbol == 17) // Repeat zero 3..10 times
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{
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codeLength = 0;
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// 3 bits + 3, [3..10]
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while (!input.TryGetBits(3, ref repeatCount, 3)) yield return false;
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}
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else // (symbol == 18), Repeat zero 11..138 times
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{
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codeLength = 0;
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// 7 bits + 11, [11..138]
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while (!input.TryGetBits(7, ref repeatCount, 11)) yield return false;
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}
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if (index + repeatCount > dataCodeCount)
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throw new StreamDecodingException("Cannot repeat code lengths past total number of data code lengths");
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while (repeatCount-- > 0)
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codeLengths[index++] = codeLength;
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}
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}
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if (codeLengths[256] == 0)
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throw new StreamDecodingException("Inflater dynamic header end-of-block code missing");
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litLenTree = new InflaterHuffmanTree(new ArraySegment<byte>(codeLengths, 0, litLenCodeCount));
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distTree = new InflaterHuffmanTree(new ArraySegment<byte>(codeLengths, litLenCodeCount, distanceCodeCount));
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yield return true;
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}
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/// <summary>
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/// Get literal/length huffman tree, must not be used before <see cref="AttemptRead"/> has returned true
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/// </summary>
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/// <exception cref="StreamDecodingException">If hader has not been successfully read by the state machine</exception>
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public InflaterHuffmanTree LiteralLengthTree
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=> litLenTree ?? throw new StreamDecodingException("Header properties were accessed before header had been successfully read");
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/// <summary>
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/// Get distance huffman tree, must not be used before <see cref="AttemptRead"/> has returned true
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/// </summary>
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/// <exception cref="StreamDecodingException">If hader has not been successfully read by the state machine</exception>
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public InflaterHuffmanTree DistanceTree
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=> distTree ?? throw new StreamDecodingException("Header properties were accessed before header had been successfully read");
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#region Instance Fields
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private readonly StreamManipulator input;
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private readonly IEnumerator<bool> state;
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private readonly IEnumerable<bool> stateMachine;
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private byte[] codeLengths = new byte[CODELEN_MAX];
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private InflaterHuffmanTree litLenTree;
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private InflaterHuffmanTree distTree;
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private int litLenCodeCount, distanceCodeCount, metaCodeCount;
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#endregion Instance Fields
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}
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}
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