// InflaterHuffmanTree.cs
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// Copyright (C) 2001 Mike Krueger
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//
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// This file was translated from java, it was part of the GNU Classpath
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// Copyright (C) 2001 Free Software Foundation, Inc.
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License
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// as published by the Free Software Foundation; either version 2
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// of the License, or (at your option) any later version.
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//
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// This program 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 General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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//
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// Linking this library statically or dynamically with other modules is
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// making a combined work based on this library. Thus, the terms and
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// conditions of the GNU General Public License cover the whole
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// combination.
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//
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// As a special exception, the copyright holders of this library give you
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// permission to link this library with independent modules to produce an
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// executable, regardless of the license terms of these independent
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// modules, and to copy and distribute the resulting executable under
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// terms of your choice, provided that you also meet, for each linked
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// independent module, the terms and conditions of the license of that
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// module. An independent module is a module which is not derived from
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// or based on this library. If you modify this library, you may extend
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// this exception to your version of the library, but you are not
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// obligated to do so. If you do not wish to do so, delete this
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// exception statement from your version.
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using System;
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using ICSharpCode.SharpZipLib.Zip.Compression.Streams;
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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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const int MAX_BITLEN = 15;
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#endregion
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#region Instance Fields
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short[] tree;
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#endregion
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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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byte[] codeLengths = new byte[288];
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int i = 0;
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while (i < 144) {
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codeLengths[i++] = 8;
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}
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while (i < 256) {
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codeLengths[i++] = 9;
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}
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while (i < 280) {
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codeLengths[i++] = 7;
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}
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while (i < 288) {
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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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codeLengths[i++] = 5;
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}
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defDistTree = new InflaterHuffmanTree(codeLengths);
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} catch (Exception) {
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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(byte[] codeLengths)
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{
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BuildTree(codeLengths);
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}
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#endregion
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void BuildTree(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.Length; i++) {
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int bits = codeLengths[i];
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if (bits > 0) {
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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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nextCode[bits] = code;
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code += blCount[bits] << (16 - bits);
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if (bits >= 10) {
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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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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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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.Length; i++) {
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int bits = codeLengths[i];
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if (bits == 0) {
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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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do {
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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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} else {
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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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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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if ((symbol = tree[lookahead]) >= 0) {
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input.DropBits(symbol & 15);
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return symbol >> 4;
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}
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int subtree = -(symbol >> 4);
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int bitlen = symbol & 15;
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if ((lookahead = input.PeekBits(bitlen)) >= 0) {
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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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} else {
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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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input.DropBits(symbol & 15);
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return symbol >> 4;
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} else {
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return -1;
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}
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}
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} else {
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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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input.DropBits(symbol & 15);
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return symbol >> 4;
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} else {
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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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