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| 1 | +/* | |
| 2 | + * Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved. | |
| 3 | + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
| 4 | + * | |
| 5 | + * This code is free software; you can redistribute it and/or modify it | |
| 6 | + * under the terms of the GNU General Public License version 2 only, as | |
| 7 | + * published by the Free Software Foundation. Oracle designates this | |
| 8 | + * particular file as subject to the "Classpath" exception as provided | |
| 9 | + * by Oracle in the LICENSE file that accompanied this code. | |
| 10 | + * | |
| 11 | + * This code is distributed in the hope that it will be useful, but WITHOUT | |
| 12 | + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
| 13 | + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
| 14 | + * version 2 for more details (a copy is included in the LICENSE file that | |
| 15 | + * accompanied this code). | |
| 16 | + * | |
| 17 | + * You should have received a copy of the GNU General Public License version | |
| 18 | + * 2 along with this work; if not, write to the Free Software Foundation, | |
| 19 | + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
| 20 | + * | |
| 21 | + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
| 22 | + * or visit www.oracle.com if you need additional information or have any | |
| 23 | + * questions. | |
| 24 | + */ | |
| 25 | + | |
| 26 | +package com.sun.imageio.plugins.common; | |
| 27 | + | |
| 28 | +import java.io.PrintStream; | |
| 29 | + | |
| 30 | +/** | |
| 31 | + * General purpose LZW String Table. | |
| 32 | + * Extracted from GIFEncoder by Adam Doppelt | |
| 33 | + * Comments added by Robin Luiten | |
| 34 | + * <code>expandCode</code> added by Robin Luiten | |
| 35 | + * The strLen table to give quick access to the lenght of an expanded | |
| 36 | + * code for use by the <code>expandCode</code> method added by Robin. | |
| 37 | + **/ | |
| 38 | +public class LZWStringTable { | |
| 39 | + /** codesize + Reserved Codes */ | |
| 40 | + private final static int RES_CODES = 2; | |
| 41 | + | |
| 42 | + private final static short HASH_FREE = (short)0xFFFF; | |
| 43 | + private final static short NEXT_FIRST = (short)0xFFFF; | |
| 44 | + | |
| 45 | + private final static int MAXBITS = 12; | |
| 46 | + private final static int MAXSTR = (1 << MAXBITS); | |
| 47 | + | |
| 48 | + private final static short HASHSIZE = 9973; | |
| 49 | + private final static short HASHSTEP = 2039; | |
| 50 | + | |
| 51 | + byte[] strChr; // after predecessor character | |
| 52 | + short[] strNxt; // predecessor string | |
| 53 | + short[] strHsh; // hash table to find predecessor + char pairs | |
| 54 | + short numStrings; // next code if adding new prestring + char | |
| 55 | + | |
| 56 | + /* | |
| 57 | + * each entry corresponds to a code and contains the length of data | |
| 58 | + * that the code expands to when decoded. | |
| 59 | + */ | |
| 60 | + int[] strLen; | |
| 61 | + | |
| 62 | + /* | |
| 63 | + * Constructor allocate memory for string store data | |
| 64 | + */ | |
| 65 | + public LZWStringTable() { | |
| 66 | + strChr = new byte[MAXSTR]; | |
| 67 | + strNxt = new short[MAXSTR]; | |
| 68 | + strLen = new int[MAXSTR]; | |
| 69 | + strHsh = new short[HASHSIZE]; | |
| 70 | + } | |
| 71 | + | |
| 72 | + /* | |
| 73 | + * @param index value of -1 indicates no predecessor [used in initialisation] | |
| 74 | + * @param b the byte [character] to add to the string store which follows | |
| 75 | + * the predecessor string specified the index. | |
| 76 | + * @return 0xFFFF if no space in table left for addition of predecesor | |
| 77 | + * index and byte b. Else return the code allocated for combination index + b. | |
| 78 | + */ | |
| 79 | + public int addCharString(short index, byte b) { | |
| 80 | + int hshidx; | |
| 81 | + | |
| 82 | + if (numStrings >= MAXSTR) { // if used up all codes | |
| 83 | + return 0xFFFF; | |
| 84 | + } | |
| 85 | + | |
| 86 | + hshidx = hash(index, b); | |
| 87 | + while (strHsh[hshidx] != HASH_FREE) { | |
| 88 | + hshidx = (hshidx + HASHSTEP) % HASHSIZE; | |
| 89 | + } | |
| 90 | + | |
| 91 | + strHsh[hshidx] = numStrings; | |
| 92 | + strChr[numStrings] = b; | |
| 93 | + if (index == HASH_FREE) { | |
| 94 | + strNxt[numStrings] = NEXT_FIRST; | |
| 95 | + strLen[numStrings] = 1; | |
| 96 | + } else { | |
| 97 | + strNxt[numStrings] = index; | |
| 98 | + strLen[numStrings] = strLen[index] + 1; | |
| 99 | + } | |
| 100 | + | |
| 101 | + return numStrings++; // return the code and inc for next code | |
| 102 | + } | |
| 103 | + | |
| 104 | + /* | |
| 105 | + * @param index index to prefix string | |
| 106 | + * @param b the character that follws the index prefix | |
| 107 | + * @return b if param index is HASH_FREE. Else return the code | |
| 108 | + * for this prefix and byte successor | |
| 109 | + */ | |
| 110 | + public short findCharString(short index, byte b) { | |
| 111 | + int hshidx, nxtidx; | |
| 112 | + | |
| 113 | + if (index == HASH_FREE) { | |
| 114 | + return (short)(b & 0xFF); // Rob fixed used to sign extend | |
| 115 | + } | |
| 116 | + | |
| 117 | + hshidx = hash(index, b); | |
| 118 | + while ((nxtidx = strHsh[hshidx]) != HASH_FREE) { // search | |
| 119 | + if (strNxt[nxtidx] == index && strChr[nxtidx] == b) { | |
| 120 | + return (short)nxtidx; | |
| 121 | + } | |
| 122 | + hshidx = (hshidx + HASHSTEP) % HASHSIZE; | |
| 123 | + } | |
| 124 | + | |
| 125 | + return (short)0xFFFF; | |
| 126 | + } | |
| 127 | + | |
| 128 | + /* | |
| 129 | + * @param codesize the size of code to be preallocated for the | |
| 130 | + * string store. | |
| 131 | + */ | |
| 132 | + public void clearTable(int codesize) { | |
| 133 | + numStrings = 0; | |
| 134 | + | |
| 135 | + for (int q = 0; q < HASHSIZE; q++) { | |
| 136 | + strHsh[q] = HASH_FREE; | |
| 137 | + } | |
| 138 | + | |
| 139 | + int w = (1 << codesize) + RES_CODES; | |
| 140 | + for (int q = 0; q < w; q++) { | |
| 141 | + addCharString((short)0xFFFF, (byte)q); // init with no prefix | |
| 142 | + } | |
| 143 | + } | |
| 144 | + | |
| 145 | + static public int hash(short index, byte lastbyte) { | |
| 146 | + return ((int)((short)(lastbyte << 8) ^ index) & 0xFFFF) % HASHSIZE; | |
| 147 | + } | |
| 148 | + | |
| 149 | + /* | |
| 150 | + * If expanded data doesn't fit into array only what will fit is written | |
| 151 | + * to buf and the return value indicates how much of the expanded code has | |
| 152 | + * been written to the buf. The next call to expandCode() should be with | |
| 153 | + * the same code and have the skip parameter set the negated value of the | |
| 154 | + * previous return. Succesive negative return values should be negated and | |
| 155 | + * added together for next skip parameter value with same code. | |
| 156 | + * | |
| 157 | + * @param buf buffer to place expanded data into | |
| 158 | + * @param offset offset to place expanded data | |
| 159 | + * @param code the code to expand to the byte array it represents. | |
| 160 | + * PRECONDITION This code must already be in the LZSS | |
| 161 | + * @param skipHead is the number of bytes at the start of the expanded code to | |
| 162 | + * be skipped before data is written to buf. It is possible that skipHead is | |
| 163 | + * equal to codeLen. | |
| 164 | + * @return the length of data expanded into buf. If the expanded code is longer | |
| 165 | + * than space left in buf then the value returned is a negative number which when | |
| 166 | + * negated is equal to the number of bytes that were used of the code being expanded. | |
| 167 | + * This negative value also indicates the buffer is full. | |
| 168 | + */ | |
| 169 | + public int expandCode(byte[] buf, int offset, short code, int skipHead) { | |
| 170 | + if (offset == -2) { | |
| 171 | + if (skipHead == 1) { | |
| 172 | + skipHead = 0; | |
| 173 | + } | |
| 174 | + } | |
| 175 | + if (code == (short)0xFFFF || // just in case | |
| 176 | + skipHead == strLen[code]) // DONE no more unpacked | |
| 177 | + { | |
| 178 | + return 0; | |
| 179 | + } | |
| 180 | + | |
| 181 | + int expandLen; // how much data we are actually expanding | |
| 182 | + int codeLen = strLen[code] - skipHead; // length of expanded code left | |
| 183 | + int bufSpace = buf.length - offset; // how much space left | |
| 184 | + if (bufSpace > codeLen) { | |
| 185 | + expandLen = codeLen; // only got this many to unpack | |
| 186 | + } else { | |
| 187 | + expandLen = bufSpace; | |
| 188 | + } | |
| 189 | + | |
| 190 | + int skipTail = codeLen - expandLen; // only > 0 if codeLen > bufSpace [left overs] | |
| 191 | + | |
| 192 | + int idx = offset + expandLen; // initialise to exclusive end address of buffer area | |
| 193 | + | |
| 194 | + // NOTE: data unpacks in reverse direction and we are placing the | |
| 195 | + // unpacked data directly into the array in the correct location. | |
| 196 | + while ((idx > offset) && (code != (short)0xFFFF)) { | |
| 197 | + if (--skipTail < 0) { // skip required of expanded data | |
| 198 | + buf[--idx] = strChr[code]; | |
| 199 | + } | |
| 200 | + code = strNxt[code]; // to predecessor code | |
| 201 | + } | |
| 202 | + | |
| 203 | + if (codeLen > expandLen) { | |
| 204 | + return -expandLen; // indicate what part of codeLen used | |
| 205 | + } else { | |
| 206 | + return expandLen; // indicate length of dat unpacked | |
| 207 | + } | |
| 208 | + } | |
| 209 | + | |
| 210 | + public void dump(PrintStream out) { | |
| 211 | + int i; | |
| 212 | + for (i = 258; i < numStrings; ++i) { | |
| 213 | + out.println(" strNxt[" + i + "] = " + strNxt[i] | |
| 214 | + + " strChr " + Integer.toHexString(strChr[i] & 0xFF) | |
| 215 | + + " strLen " + Integer.toHexString(strLen[i])); | |
| 216 | + } | |
| 217 | + } | |
| 218 | +} | |