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 agsXMPP.IO.Compression.Streams;
41 
42 namespace agsXMPP.IO.Compression
43 {
44 
45 	/// <summary>
46 	/// Huffman tree used for inflation
47 	/// </summary>
48 	public class InflaterHuffmanTree
49 	{
50 		static int MAX_BITLEN = 15;
51 		short[] tree;
52 
53 		/// <summary>
54 		/// Literal length tree
55 		/// </summary>
56 		public static InflaterHuffmanTree defLitLenTree;
57 
58 		/// <summary>
59 		/// Distance tree
60 		/// </summary>
61 		public static InflaterHuffmanTree defDistTree;
62 
InflaterHuffmanTree()63 		static InflaterHuffmanTree()
64 		{
65 			try {
66 				byte[] codeLengths = new byte[288];
67 				int i = 0;
68 				while (i < 144) {
69 					codeLengths[i++] = 8;
70 				}
71 				while (i < 256) {
72 					codeLengths[i++] = 9;
73 				}
74 				while (i < 280) {
75 					codeLengths[i++] = 7;
76 				}
77 				while (i < 288) {
78 					codeLengths[i++] = 8;
79 				}
80 				defLitLenTree = new InflaterHuffmanTree(codeLengths);
81 
82 				codeLengths = new byte[32];
83 				i = 0;
84 				while (i < 32) {
85 					codeLengths[i++] = 5;
86 				}
87 				defDistTree = new InflaterHuffmanTree(codeLengths);
88 			} catch (Exception) {
89 				throw new SharpZipBaseException("InflaterHuffmanTree: static tree length illegal");
90 			}
91 		}
92 
93 		/// <summary>
94 		/// Constructs a Huffman tree from the array of code lengths.
95 		/// </summary>
96 		/// <param name = "codeLengths">
97 		/// the array of code lengths
98 		/// </param>
InflaterHuffmanTree(byte[] codeLengths)99 		public InflaterHuffmanTree(byte[] codeLengths)
100 		{
101 			BuildTree(codeLengths);
102 		}
103 
BuildTree(byte[] codeLengths)104 		void BuildTree(byte[] codeLengths)
105 		{
106 			int[] blCount  = new int[MAX_BITLEN + 1];
107 			int[] nextCode = new int[MAX_BITLEN + 1];
108 
109 			for (int i = 0; i < codeLengths.Length; i++) {
110 				int bits = codeLengths[i];
111 				if (bits > 0) {
112 					blCount[bits]++;
113 				}
114 			}
115 
116 			int code = 0;
117 			int treeSize = 512;
118 			for (int bits = 1; bits <= MAX_BITLEN; bits++) {
119 				nextCode[bits] = code;
120 				code += blCount[bits] << (16 - bits);
121 				if (bits >= 10) {
122 					/* We need an extra table for bit lengths >= 10. */
123 					int start = nextCode[bits] & 0x1ff80;
124 					int end   = code & 0x1ff80;
125 					treeSize += (end - start) >> (16 - bits);
126 				}
127 			}
128 
129 /* -jr comment this out! doesnt work for dynamic trees and pkzip 2.04g
130 			if (code != 65536)
131 			{
132 				throw new SharpZipBaseException("Code lengths don't add up properly.");
133 			}
134 */
135 			/* Now create and fill the extra tables from longest to shortest
136 			* bit len.  This way the sub trees will be aligned.
137 			*/
138 			tree = new short[treeSize];
139 			int treePtr = 512;
140 			for (int bits = MAX_BITLEN; bits >= 10; bits--) {
141 				int end   = code & 0x1ff80;
142 				code -= blCount[bits] << (16 - bits);
143 				int start = code & 0x1ff80;
144 				for (int i = start; i < end; i += 1 << 7) {
145 					tree[DeflaterHuffman.BitReverse(i)] = (short) ((-treePtr << 4) | bits);
146 					treePtr += 1 << (bits-9);
147 				}
148 			}
149 
150 			for (int i = 0; i < codeLengths.Length; i++) {
151 				int bits = codeLengths[i];
152 				if (bits == 0) {
153 					continue;
154 				}
155 				code = nextCode[bits];
156 				int revcode = DeflaterHuffman.BitReverse(code);
157 				if (bits <= 9) {
158 					do {
159 						tree[revcode] = (short) ((i << 4) | bits);
160 						revcode += 1 << bits;
161 					} while (revcode < 512);
162 				} else {
163 					int subTree = tree[revcode & 511];
164 					int treeLen = 1 << (subTree & 15);
165 					subTree = -(subTree >> 4);
166 					do {
167 						tree[subTree | (revcode >> 9)] = (short) ((i << 4) | bits);
168 						revcode += 1 << bits;
169 					} while (revcode < treeLen);
170 				}
171 				nextCode[bits] = code + (1 << (16 - bits));
172 			}
173 
174 		}
175 
176 		/// <summary>
177 		/// Reads the next symbol from input.  The symbol is encoded using the
178 		/// huffman tree.
179 		/// </summary>
180 		/// <param name="input">
181 		/// input the input source.
182 		/// </param>
183 		/// <returns>
184 		/// the next symbol, or -1 if not enough input is available.
185 		/// </returns>
GetSymbol(StreamManipulator input)186 		public int GetSymbol(StreamManipulator input)
187 		{
188 			int lookahead, symbol;
189 			if ((lookahead = input.PeekBits(9)) >= 0) {
190 				if ((symbol = tree[lookahead]) >= 0) {
191 					input.DropBits(symbol & 15);
192 					return symbol >> 4;
193 				}
194 				int subtree = -(symbol >> 4);
195 				int bitlen = symbol & 15;
196 				if ((lookahead = input.PeekBits(bitlen)) >= 0) {
197 					symbol = tree[subtree | (lookahead >> 9)];
198 					input.DropBits(symbol & 15);
199 					return symbol >> 4;
200 				} else {
201 					int bits = input.AvailableBits;
202 					lookahead = input.PeekBits(bits);
203 					symbol = tree[subtree | (lookahead >> 9)];
204 					if ((symbol & 15) <= bits) {
205 						input.DropBits(symbol & 15);
206 						return symbol >> 4;
207 					} else {
208 						return -1;
209 					}
210 				}
211 			} else {
212 				int bits = input.AvailableBits;
213 				lookahead = input.PeekBits(bits);
214 				symbol = tree[lookahead];
215 				if (symbol >= 0 && (symbol & 15) <= bits) {
216 					input.DropBits(symbol & 15);
217 					return symbol >> 4;
218 				} else {
219 					return -1;
220 				}
221 			}
222 		}
223 	}
224 }
225 
226