238 lines
5.1 KiB
C#
238 lines
5.1 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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/// <summary>
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/// Huffman tree used for inflation
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/// </summary>
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public class InflaterHuffmanTree
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{
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#region Constants
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private const int MAX_BITLEN = 15;
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#endregion Constants
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#region Instance Fields
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private short[] tree;
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#endregion Instance Fields
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/// <summary>
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/// Literal length tree
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/// </summary>
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public static InflaterHuffmanTree defLitLenTree;
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/// <summary>
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/// Distance tree
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/// </summary>
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public static InflaterHuffmanTree defDistTree;
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static InflaterHuffmanTree()
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{
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try
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{
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byte[] codeLengths = new byte[288];
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int i = 0;
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while (i < 144)
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{
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codeLengths[i++] = 8;
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}
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while (i < 256)
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{
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codeLengths[i++] = 9;
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}
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while (i < 280)
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{
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codeLengths[i++] = 7;
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}
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while (i < 288)
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{
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codeLengths[i++] = 8;
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}
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defLitLenTree = new InflaterHuffmanTree(codeLengths);
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codeLengths = new byte[32];
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i = 0;
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while (i < 32)
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{
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codeLengths[i++] = 5;
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}
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defDistTree = new InflaterHuffmanTree(codeLengths);
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}
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catch (Exception)
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{
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throw new SharpZipBaseException("InflaterHuffmanTree: static tree length illegal");
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}
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}
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#region Constructors
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/// <summary>
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/// Constructs a Huffman tree from the array of code lengths.
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/// </summary>
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/// <param name = "codeLengths">
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/// the array of code lengths
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/// </param>
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public InflaterHuffmanTree(IList<byte> codeLengths)
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{
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BuildTree(codeLengths);
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}
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#endregion Constructors
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private void BuildTree(IList<byte> codeLengths)
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{
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int[] blCount = new int[MAX_BITLEN + 1];
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int[] nextCode = new int[MAX_BITLEN + 1];
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for (int i = 0; i < codeLengths.Count; i++)
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{
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int bits = codeLengths[i];
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if (bits > 0)
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{
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blCount[bits]++;
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}
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}
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int code = 0;
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int treeSize = 512;
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for (int bits = 1; bits <= MAX_BITLEN; bits++)
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{
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nextCode[bits] = code;
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code += blCount[bits] << (16 - bits);
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if (bits >= 10)
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{
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/* We need an extra table for bit lengths >= 10. */
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int start = nextCode[bits] & 0x1ff80;
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int end = code & 0x1ff80;
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treeSize += (end - start) >> (16 - bits);
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}
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}
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/* -jr comment this out! doesnt work for dynamic trees and pkzip 2.04g
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if (code != 65536)
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{
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throw new SharpZipBaseException("Code lengths don't add up properly.");
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}
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*/
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/* Now create and fill the extra tables from longest to shortest
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* bit len. This way the sub trees will be aligned.
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*/
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tree = new short[treeSize];
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int treePtr = 512;
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for (int bits = MAX_BITLEN; bits >= 10; bits--)
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{
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int end = code & 0x1ff80;
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code -= blCount[bits] << (16 - bits);
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int start = code & 0x1ff80;
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for (int i = start; i < end; i += 1 << 7)
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{
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tree[DeflaterHuffman.BitReverse(i)] = (short)((-treePtr << 4) | bits);
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treePtr += 1 << (bits - 9);
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}
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}
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for (int i = 0; i < codeLengths.Count; i++)
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{
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int bits = codeLengths[i];
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if (bits == 0)
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{
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continue;
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}
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code = nextCode[bits];
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int revcode = DeflaterHuffman.BitReverse(code);
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if (bits <= 9)
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{
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do
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{
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tree[revcode] = (short)((i << 4) | bits);
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revcode += 1 << bits;
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} while (revcode < 512);
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}
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else
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{
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int subTree = tree[revcode & 511];
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int treeLen = 1 << (subTree & 15);
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subTree = -(subTree >> 4);
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do
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{
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tree[subTree | (revcode >> 9)] = (short)((i << 4) | bits);
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revcode += 1 << bits;
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} while (revcode < treeLen);
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}
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nextCode[bits] = code + (1 << (16 - bits));
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}
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}
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/// <summary>
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/// Reads the next symbol from input. The symbol is encoded using the
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/// huffman tree.
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/// </summary>
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/// <param name="input">
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/// input the input source.
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/// </param>
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/// <returns>
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/// the next symbol, or -1 if not enough input is available.
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/// </returns>
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public int GetSymbol(StreamManipulator input)
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{
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int lookahead, symbol;
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if ((lookahead = input.PeekBits(9)) >= 0)
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{
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symbol = tree[lookahead];
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int bitlen = symbol & 15;
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if (symbol >= 0)
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{
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if(bitlen == 0){
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throw new SharpZipBaseException("Encountered invalid codelength 0");
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}
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input.DropBits(bitlen);
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return symbol >> 4;
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}
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int subtree = -(symbol >> 4);
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if ((lookahead = input.PeekBits(bitlen)) >= 0)
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{
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symbol = tree[subtree | (lookahead >> 9)];
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input.DropBits(symbol & 15);
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return symbol >> 4;
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}
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else
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{
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int bits = input.AvailableBits;
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lookahead = input.PeekBits(bits);
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symbol = tree[subtree | (lookahead >> 9)];
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if ((symbol & 15) <= bits)
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{
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input.DropBits(symbol & 15);
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return symbol >> 4;
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}
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else
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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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else // Less than 9 bits
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{
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int bits = input.AvailableBits;
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lookahead = input.PeekBits(bits);
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symbol = tree[lookahead];
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if (symbol >= 0 && (symbol & 15) <= bits)
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{
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input.DropBits(symbol & 15);
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return symbol >> 4;
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}
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else
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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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}
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