root/branches/Abonament/BazaReklam.Updater/ICSharpCode.SharpZipLib/Zip/Compression/InflaterHuffmanTree.cs @ 769

// InflaterHuffmanTree.cs
// Copyright (C) 2001 Mike Krueger
//
// This file was translated from java, it was part of the GNU Classpath
// Copyright (C) 2001 Free Software Foundation, Inc.
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License
// as published by the Free Software Foundation; either version 2
// of the License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
//
// Linking this library statically or dynamically with other modules is
// making a combined work based on this library.  Thus, the terms and
// conditions of the GNU General Public License cover the whole
// combination.
// 
// As a special exception, the copyright holders of this library give you
// permission to link this library with independent modules to produce an
// executable, regardless of the license terms of these independent
// modules, and to copy and distribute the resulting executable under
// terms of your choice, provided that you also meet, for each linked
// independent module, the terms and conditions of the license of that
// module.  An independent module is a module which is not derived from
// or based on this library.  If you modify this library, you may extend
// this exception to your version of the library, but you are not
// obligated to do so.  If you do not wish to do so, delete this
// exception statement from your version.

using System;

using ICSharpCode.SharpZipLib.Zip.Compression.Streams;

namespace ICSharpCode.SharpZipLib.Zip.Compression 
{
        
        /// <summary>
        /// Huffman tree used for inflation
        /// </summary>
        public class InflaterHuffmanTree
        {
                #region Constants
                const int MAX_BITLEN = 15;
                #endregion

                #region Instance Fields
                short[] tree;
                #endregion

                /// <summary>
                /// Literal length tree
                /// </summary>
                public static InflaterHuffmanTree defLitLenTree;
                
                /// <summary>
                /// Distance tree
                /// </summary>
                public static InflaterHuffmanTree defDistTree;
                
                static InflaterHuffmanTree()
                {
                        try {
                                byte[] codeLengths = new byte[288];
                                int i = 0;
                                while (i < 144) {
                                        codeLengths[i++] = 8;
                                }
                                while (i < 256) {
                                        codeLengths[i++] = 9;
                                }
                                while (i < 280) {
                                        codeLengths[i++] = 7;
                                }
                                while (i < 288) {
                                        codeLengths[i++] = 8;
                                }
                                defLitLenTree = new InflaterHuffmanTree(codeLengths);
                                
                                codeLengths = new byte[32];
                                i = 0;
                                while (i < 32) {
                                        codeLengths[i++] = 5;
                                }
                                defDistTree = new InflaterHuffmanTree(codeLengths);
                        } catch (Exception) {
                                throw new SharpZipBaseException("InflaterHuffmanTree: static tree length illegal");
                        }
                }

                #region Constructors
                /// <summary>
                /// Constructs a Huffman tree from the array of code lengths.
                /// </summary>
                /// <param name = "codeLengths">
                /// the array of code lengths
                /// </param>
                public InflaterHuffmanTree(byte[] codeLengths)
                {
                        BuildTree(codeLengths);
                }
                #endregion

                void BuildTree(byte[] codeLengths)
                {
                        int[] blCount  = new int[MAX_BITLEN + 1];
                        int[] nextCode = new int[MAX_BITLEN + 1];
                        
                        for (int i = 0; i < codeLengths.Length; i++) {
                                int bits = codeLengths[i];
                                if (bits > 0) {
                                        blCount[bits]++;
                                }
                        }
                        
                        int code = 0;
                        int treeSize = 512;
                        for (int bits = 1; bits <= MAX_BITLEN; bits++) {
                                nextCode[bits] = code;
                                code += blCount[bits] << (16 - bits);
                                if (bits >= 10) {
                                        /* We need an extra table for bit lengths >= 10. */
                                        int start = nextCode[bits] & 0x1ff80;
                                        int end   = code & 0x1ff80;
                                        treeSize += (end - start) >> (16 - bits);
                                }
                        }
                        
/* -jr comment this out! doesnt work for dynamic trees and pkzip 2.04g
                        if (code != 65536) 
                        {
                                throw new SharpZipBaseException("Code lengths don't add up properly.");
                        }
*/
                        /* Now create and fill the extra tables from longest to shortest
                        * bit len.  This way the sub trees will be aligned.
                        */
                        tree = new short[treeSize];
                        int treePtr = 512;
                        for (int bits = MAX_BITLEN; bits >= 10; bits--) {
                                int end   = code & 0x1ff80;
                                code -= blCount[bits] << (16 - bits);
                                int start = code & 0x1ff80;
                                for (int i = start; i < end; i += 1 << 7) {
                                        tree[DeflaterHuffman.BitReverse(i)] = (short) ((-treePtr << 4) | bits);
                                        treePtr += 1 << (bits-9);
                                }
                        }
                        
                        for (int i = 0; i < codeLengths.Length; i++) {
                                int bits = codeLengths[i];
                                if (bits == 0) {
                                        continue;
                                }
                                code = nextCode[bits];
                                int revcode = DeflaterHuffman.BitReverse(code);
                                if (bits <= 9) {
                                        do {
                                                tree[revcode] = (short) ((i << 4) | bits);
                                                revcode += 1 << bits;
                                        } while (revcode < 512);
                                } else {
                                        int subTree = tree[revcode & 511];
                                        int treeLen = 1 << (subTree & 15);
                                        subTree = -(subTree >> 4);
                                        do {
                                                tree[subTree | (revcode >> 9)] = (short) ((i << 4) | bits);
                                                revcode += 1 << bits;
                                        } while (revcode < treeLen);
                                }
                                nextCode[bits] = code + (1 << (16 - bits));
                        }
                        
                }
                
                /// <summary>
                /// Reads the next symbol from input.  The symbol is encoded using the
                /// huffman tree.
                /// </summary>
                /// <param name="input">
                /// input the input source.
                /// </param>
                /// <returns>
                /// the next symbol, or -1 if not enough input is available.
                /// </returns>
                public int GetSymbol(StreamManipulator input)
                {
                        int lookahead, symbol;
                        if ((lookahead = input.PeekBits(9)) >= 0) {
                                if ((symbol = tree[lookahead]) >= 0) {
                                        input.DropBits(symbol & 15);
                                        return symbol >> 4;
                                }
                                int subtree = -(symbol >> 4);
                                int bitlen = symbol & 15;
                                if ((lookahead = input.PeekBits(bitlen)) >= 0) {
                                        symbol = tree[subtree | (lookahead >> 9)];
                                        input.DropBits(symbol & 15);
                                        return symbol >> 4;
                                } else {
                                        int bits = input.AvailableBits;
                                        lookahead = input.PeekBits(bits);
                                        symbol = tree[subtree | (lookahead >> 9)];
                                        if ((symbol & 15) <= bits) {
                                                input.DropBits(symbol & 15);
                                                return symbol >> 4;
                                        } else {
                                                return -1;
                                        }
                                }
                        } else {
                                int bits = input.AvailableBits;
                                lookahead = input.PeekBits(bits);
                                symbol = tree[lookahead];
                                if (symbol >= 0 && (symbol & 15) <= bits) {
                                        input.DropBits(symbol & 15);
                                        return symbol >> 4;
                                } else {
                                        return -1;
                                }
                        }
                }
        }
}