irc/TechBot/Compression/InflaterHuffmanTree.cs

   1 // InflaterHuffmanTree.cs
   2 // Copyright (C) 2001 Mike Krueger
   3 //
   4 // This file was translated from java, it was part of the GNU Classpath
   5 // Copyright (C) 2001 Free Software Foundation, Inc.
   6 //
   7 // This program is free software; you can redistribute it and/or
   8 // modify it under the terms of the GNU General Public License
   9 // as published by the Free Software Foundation; either version 2
  10 // of the License, or (at your option) any later version.
  11 //
  12 // This program is distributed in the hope that it will be useful,
  13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 // GNU General Public License for more details.
  16 //
  17 // You should have received a copy of the GNU General Public License
  18 // along with this program; if not, write to the Free Software
  19 // Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  20 //
  21 // Linking this library statically or dynamically with other modules is
  22 // making a combined work based on this library.  Thus, the terms and
  23 // conditions of the GNU General Public License cover the whole
  24 // combination.
  25 //
  26 // As a special exception, the copyright holders of this library give you
  27 // permission to link this library with independent modules to produce an
  28 // executable, regardless of the license terms of these independent
  29 // modules, and to copy and distribute the resulting executable under
  30 // terms of your choice, provided that you also meet, for each linked
  31 // independent module, the terms and conditions of the license of that
  32 // module.  An independent module is a module which is not derived from
  33 // or based on this library.  If you modify this library, you may extend
  34 // this exception to your version of the library, but you are not
  35 // obligated to do so.  If you do not wish to do so, delete this
  36 // exception statement from your version.
  37
  38 using System;
  39
  40 using ICSharpCode.SharpZipLib.Zip.Compression.Streams;
  41
  42 namespace ICSharpCode.SharpZipLib.Zip.Compression
  43 {
  44
  45         public class InflaterHuffmanTree
  46         {
  47                 private static int MAX_BITLEN = 15;
  48                 private short[] tree;
  49
  50                 public static InflaterHuffmanTree defLitLenTree, defDistTree;
  51
  52                 static InflaterHuffmanTree()
  53                 {
  54                         try {
  55                                 byte[] codeLengths = new byte[288];
  56                                 int i = 0;
  57                                 while (i < 144) {
  58                                         codeLengths[i++] = 8;
  59                                 }
  60                                 while (i < 256) {
  61                                         codeLengths[i++] = 9;
  62                                 }
  63                                 while (i < 280) {
  64                                         codeLengths[i++] = 7;
  65                                 }
  66                                 while (i < 288) {
  67                                         codeLengths[i++] = 8;
  68                                 }
  69                                 defLitLenTree = new InflaterHuffmanTree(codeLengths);
  70
  71                                 codeLengths = new byte[32];
  72                                 i = 0;
  73                                 while (i < 32) {
  74                                         codeLengths[i++] = 5;
  75                                 }
  76                                 defDistTree = new InflaterHuffmanTree(codeLengths);
  77                         } catch (Exception) {
  78                                 throw new ApplicationException("InflaterHuffmanTree: static tree length illegal");
  79                         }
  80                 }
  81
  82                 /// <summary>
  83                 /// Constructs a Huffman tree from the array of code lengths.
  84                 /// </summary>
  85                 /// <param name = "codeLengths">
  86                 /// the array of code lengths
  87                 /// </param>
  88                 public InflaterHuffmanTree(byte[] codeLengths)
  89                 {
  90                         BuildTree(codeLengths);
  91                 }
  92
  93                 private void BuildTree(byte[] codeLengths)
  94                 {
  95                         int[] blCount  = new int[MAX_BITLEN + 1];
  96                         int[] nextCode = new int[MAX_BITLEN + 1];
  97
  98                         for (int i = 0; i < codeLengths.Length; i++) {
  99                                 int bits = codeLengths[i];
 100                                 if (bits > 0) {
 101                                         blCount[bits]++;
 102                                 }
 103                         }
 104
 105                         int code = 0;
 106                         int treeSize = 512;
 107                         for (int bits = 1; bits <= MAX_BITLEN; bits++) {
 108                                 nextCode[bits] = code;
 109                                 code += blCount[bits] << (16 - bits);
 110                                 if (bits >= 10) {
 111                                         /* We need an extra table for bit lengths >= 10. */
 112                                         int start = nextCode[bits] & 0x1ff80;
 113                                         int end   = code & 0x1ff80;
 114                                         treeSize += (end - start) >> (16 - bits);
 115                                 }
 116                         }
 117 /* -jr comment this out! doesnt work for dynamic trees and pkzip 2.04g
 118                         if (code != 65536)
 119                         {
 120                                 throw new Exception("Code lengths don't add up properly.");
 121                         }
 122 */
 123                         /* Now create and fill the extra tables from longest to shortest
 124                         * bit len.  This way the sub trees will be aligned.
 125                         */
 126                         tree = new short[treeSize];
 127                         int treePtr = 512;
 128                         for (int bits = MAX_BITLEN; bits >= 10; bits--) {
 129                                 int end   = code & 0x1ff80;
 130                                 code -= blCount[bits] << (16 - bits);
 131                                 int start = code & 0x1ff80;
 132                                 for (int i = start; i < end; i += 1 << 7) {
 133                                         tree[DeflaterHuffman.BitReverse(i)] = (short) ((-treePtr << 4) | bits);
 134                                         treePtr += 1 << (bits-9);
 135                                 }
 136                         }
 137
 138                         for (int i = 0; i < codeLengths.Length; i++) {
 139                                 int bits = codeLengths[i];
 140                                 if (bits == 0) {
 141                                         continue;
 142                                 }
 143                                 code = nextCode[bits];
 144                                 int revcode = DeflaterHuffman.BitReverse(code);
 145                                 if (bits <= 9) {
 146                                         do {
 147                                                 tree[revcode] = (short) ((i << 4) | bits);
 148                                                 revcode += 1 << bits;
 149                                         } while (revcode < 512);
 150                                 } else {
 151                                         int subTree = tree[revcode & 511];
 152                                         int treeLen = 1 << (subTree & 15);
 153                                         subTree = -(subTree >> 4);
 154                                         do {
 155                                                 tree[subTree | (revcode >> 9)] = (short) ((i << 4) | bits);
 156                                                 revcode += 1 << bits;
 157                                         } while (revcode < treeLen);
 158                                 }
 159                                 nextCode[bits] = code + (1 << (16 - bits));
 160                         }
 161
 162                 }
 163
 164                 /// <summary>
 165                 /// Reads the next symbol from input.  The symbol is encoded using the
 166                 /// huffman tree.
 167                 /// </summary>
 168                 /// <param name="input">
 169                 /// input the input source.
 170                 /// </param>
 171                 /// <returns>
 172                 /// the next symbol, or -1 if not enough input is available.
 173                 /// </returns>
 174                 public int GetSymbol(StreamManipulator input)
 175                 {
 176                         int lookahead, symbol;
 177                         if ((lookahead = input.PeekBits(9)) >= 0) {
 178                                 if ((symbol = tree[lookahead]) >= 0) {
 179                                         input.DropBits(symbol & 15);
 180                                         return symbol >> 4;
 181                                 }
 182                                 int subtree = -(symbol >> 4);
 183                                 int bitlen = symbol & 15;
 184                                 if ((lookahead = input.PeekBits(bitlen)) >= 0) {
 185                                         symbol = tree[subtree | (lookahead >> 9)];
 186                                         input.DropBits(symbol & 15);
 187                                         return symbol >> 4;
 188                                 } else {
 189                                         int bits = input.AvailableBits;
 190                                         lookahead = input.PeekBits(bits);
 191                                         symbol = tree[subtree | (lookahead >> 9)];
 192                                         if ((symbol & 15) <= bits) {
 193                                                 input.DropBits(symbol & 15);
 194                                                 return symbol >> 4;
 195                                         } else {
 196                                                 return -1;
 197                                         }
 198                                 }
 199                         } else {
 200                                 int bits = input.AvailableBits;
 201                                 lookahead = input.PeekBits(bits);
 202                                 symbol = tree[lookahead];
 203                                 if (symbol >= 0 && (symbol & 15) <= bits) {
 204                                         input.DropBits(symbol & 15);
 205                                         return symbol >> 4;
 206                                 } else {
 207                                         return -1;
 208                                 }
 209                         }
 210                 }
 211         }
 212 }
 213