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常用工具集/Utility/ICSharpCode.SharpZipLib/Zip/Compression/InflaterDynHeader.cs

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