LZWDecoder


1   /*
2    * Copyright (c) 2001 Sun Microsystems, Inc. All Rights Reserved.
3    *
4    * Redistribution and use in source and binary forms, with or without
5    * modification, are permitted provided that the following conditions are met:
6    *
7    * -Redistributions of source code must retain the above copyright notice, this
8    * list of conditions and the following disclaimer.
9    *
10   * -Redistribution in binary form must reproduct the above copyright notice,
11   * this list of conditions and the following disclaimer in the documentation
12   * and/or other materials provided with the distribution.
13   *
14   * Neither the name of Sun Microsystems, Inc. or the names of contributors may
15   * be used to endorse or promote products derived from this software without
16   * specific prior written permission.
17   *
18   * This software is provided "AS IS," without a warranty of any kind. ALL
19   * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING ANY
20   * IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR
21   * NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE
22   * LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING
23   * OR DISTRIBUTING THE SOFTWARE OR ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS
24   * LICENSORS BE LIABLE FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT,
25   * INDIRECT, SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
26   * CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF THE USE OF
27   * OR INABILITY TO USE SOFTWARE, EVEN IF SUN HAS BEEN ADVISED OF THE
28   * POSSIBILITY OF SUCH DAMAGES.
29   *
30   * You acknowledge that Software is not designed,licensed or intended for use in
31   * the design, construction, operation or maintenance of any nuclear facility.
32   *
33   * Adapted from the JAI codecs TIFFLZWDecoder.
34   */
35  package com.lowagie.text.pdf;
36  import java.io.IOException  ;
37  import java.io.OutputStream  ;
38  
39  import com.lowagie.text.ExceptionConverter;
40  /**
41   * A class for performing LZW decoding.
42   *
43   *
44   */
45  public class LZWDecoder {
46      
47      byte stringTable[][];
48      byte data[] = null;
49      OutputStream   uncompData;
50      int tableIndex, bitsToGet = 9;
51      int bytePointer, bitPointer;
52      int nextData = 0;
53      int nextBits = 0;
54      
55      int andTable[] = {
56          511,
57          1023,
58          2047,
59          4095
60      };
61      
62      public LZWDecoder() {
63      }
64      
65      /**
66       * Method to decode LZW compressed data.
67       *
68       * @param data            The compressed data.
69       * @param uncompData      Array to return the uncompressed data in.
70       */
71      public void decode(byte data[], OutputStream   uncompData) {
72          
73          if(data[0] == (byte)0x00 && data[1] == (byte)0x01) {
74              throw new RuntimeException  ("LZW flavour not supported.");
75          }
76          
77          initializeStringTable();
78          
79          this.data = data;
80          this.uncompData = uncompData;
81          
82          // Initialize pointers
83          bytePointer = 0;
84          bitPointer = 0;
85          
86          nextData = 0;
87          nextBits = 0;
88          
89          int code, oldCode = 0;
90          byte string[];
91          
92          while ((code = getNextCode()) != 257) {
93              
94              if (code == 256) {
95                  
96                  initializeStringTable();
97                  code = getNextCode();
98                  
99                  if (code == 257) {
100                     break;
101                 }
102                 
103                 writeString(stringTable[code]);
104                 oldCode = code;
105                 
106             } else {
107                 
108                 if (code < tableIndex) {
109                     
110                     string = stringTable[code];
111                     
112                     writeString(string);
113                     addStringToTable(stringTable[oldCode], string[0]);
114                     oldCode = code;
115                     
116                 } else {
117                     
118                     string = stringTable[oldCode];
119                     string = composeString(string, string[0]);
120                     writeString(string);
121                     addStringToTable(string);
122                     oldCode = code;
123                 }
124             }
125         }
126     }
127     
128     
129     /**
130      * Initialize the string table.
131      */
132     public void initializeStringTable() {
133         
134         stringTable = new byte[8192][];
135         
136         for (int i=0; i<256; i++) {
137             stringTable[i] = new byte[1];
138             stringTable[i][0] = (byte)i;
139         }
140         
141         tableIndex = 258;
142         bitsToGet = 9;
143     }
144     
145     /**
146      * Write out the string just uncompressed.
147      */
148     public void writeString(byte string[]) {
149         try {
150             uncompData.write(string);
151         }
152         catch (IOException   e) {
153             throw new ExceptionConverter(e);
154         }
155     }
156     
157     /**
158      * Add a new string to the string table.
159      */
160     public void addStringToTable(byte oldString[], byte newString) {
161         int length = oldString.length;
162         byte string[] = new byte[length + 1];
163         System.arraycopy(oldString, 0, string, 0, length);
164         string[length] = newString;
165         
166         // Add this new String to the table
167         stringTable[tableIndex++] = string;
168         
169         if (tableIndex == 511) {
170             bitsToGet = 10;
171         } else if (tableIndex == 1023) {
172             bitsToGet = 11;
173         } else if (tableIndex == 2047) {
174             bitsToGet = 12;
175         }
176     }
177     
178     /**
179      * Add a new string to the string table.
180      */
181     public void addStringToTable(byte string[]) {
182         
183         // Add this new String to the table
184         stringTable[tableIndex++] = string;
185         
186         if (tableIndex == 511) {
187             bitsToGet = 10;
188         } else if (tableIndex == 1023) {
189             bitsToGet = 11;
190         } else if (tableIndex == 2047) {
191             bitsToGet = 12;
192         }
193     }
194     
195     /**
196      * Append <code>newString</code> to the end of <code>oldString</code>.
197      */
198     public byte[] composeString(byte oldString[], byte newString) {
199         int length = oldString.length;
200         byte string[] = new byte[length + 1];
201         System.arraycopy(oldString, 0, string, 0, length);
202         string[length] = newString;
203         
204         return string;
205     }
206     
207     // Returns the next 9, 10, 11 or 12 bits
208     public int getNextCode() {
209         // Attempt to get the next code. The exception is caught to make
210         // this robust to cases wherein the EndOfInformation code has been
211         // omitted from a strip. Examples of such cases have been observed
212         // in practice.
213         try {
214             nextData = (nextData << 8) | (data[bytePointer++] & 0xff);
215             nextBits += 8;
216             
217             if (nextBits < bitsToGet) {
218                 nextData = (nextData << 8) | (data[bytePointer++] & 0xff);
219                 nextBits += 8;
220             }
221             
222             int code =
223             (nextData >> (nextBits - bitsToGet)) & andTable[bitsToGet-9];
224             nextBits -= bitsToGet;
225             
226             return code;
227         } catch(ArrayIndexOutOfBoundsException   e) {
228             // Strip not terminated as expected: return EndOfInformation code.
229             return 257;
230         }
231     }
232 }
233
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