LZWDictionary


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9    *    this list of conditions and the following disclaimer.
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31  package org.pdfbox.filter;
32  
33  import java.io.ByteArrayOutputStream  ;
34  import java.io.IOException  ;
35  
36  import java.util.HashMap  ;
37  import java.util.Map  ;
38  
39  /**
40   * This is the used for the LZWDecode filter.  This represents the dictionary mappings
41   * between codes and their values.
42   *
43   * @author <a HREF="mailto:ben@benlitchfield.com">Ben Litchfield</a>
44   * @version $Revision: 1.4 $
45   */
46  class LZWDictionary
47  {
48      private Map   codeToData = new HashMap  ();
49      private LZWNode root = new LZWNode();
50  
51      private ByteArrayOutputStream   buffer = new ByteArrayOutputStream  ();
52      private long nextCode = 258;
53      private int codeSize = 9;
54  
55      /**
56       * constructor.
57       */
58      public LZWDictionary()
59      {
60          for( long i=0; i<256; i++ )
61          {
62              LZWNode node = new LZWNode();
63              node.setCode( i );
64              root.setNode( (byte)i, node );
65              codeToData.put( new Long  ( i ), new byte[]{ (byte)i } );
66          }
67      }
68  
69      /**
70       * This will get the value for the code.  It will return null if the code is not
71       * defined.
72       *
73       * @param code The key to the data.
74       *
75       * @return The data that is mapped to the code.
76       */
77      public byte[] getData( long code )
78      {
79          return (byte[])codeToData.get( new Long  ( code ) );
80      }
81  
82      /**
83       * This will take a visit from a byte[].  This will create new code entries as
84       * necessary.
85       *
86       * @param data The byte to get a visit from.
87       *
88       * @throws IOException If there is an error visiting this data.
89       */
90      public void visit( byte[] data ) throws IOException  
91      {
92          for( int i=0; i<data.length; i++ )
93          {
94              visit( data[i] );
95          }
96      }
97  
98      /**
99       * This will take a visit from a byte.  This will create new code entries as
100      * necessary.
101      *
102      * @param data The byte to get a visit from.
103      *
104      * @throws IOException If there is an error visiting this data.
105      */
106     public void visit( byte data ) throws IOException  
107     {
108         buffer.write( data );
109         byte[] curBuffer = buffer.toByteArray();
110         LZWNode previous = null;
111         LZWNode current = root;
112         boolean createNewCode = false;
113         for( int i=0; i<curBuffer.length && current != null; i++ )
114         {
115             previous = current;
116             current = current.getNode( curBuffer[i] );
117             if( current == null )
118             {
119                 createNewCode = true;
120                 current = new LZWNode();
121                 previous.setNode( curBuffer[i], current );
122             }
123         }
124         if( createNewCode )
125         {
126             long code = nextCode++;
127             current.setCode( code );
128             codeToData.put( new Long  ( code ), curBuffer );
129 
130             /**
131             System.out.print( "Adding " + code + "='" );
132             for( int i=0; i<curBuffer.length; i++ )
133             {
134                 String hex = Integer.toHexString( ((curBuffer[i]+256)%256) );
135                 if( hex.length() <=1 )
136                 {
137                     hex = "0" + hex;
138                 }
139                 if( i != curBuffer.length -1 )
140                 {
141                     hex += " ";
142                 }
143                 System.out.print( hex.toUpperCase() );
144             }
145             System.out.println( "'" );
146             **/
147             buffer.reset();
148             buffer.write( data );
149             resetCodeSize();
150         }
151     }
152 
153     /**
154      * This will get the next code that will be created.
155      *
156      * @return The next code to be created.
157      */
158     public long getNextCode()
159     {
160         return nextCode;
161     }
162 
163     /**
164      * This will get the size of the code in bits, 9, 10, or 11.
165      *
166      * @return The size of the code in bits.
167      */
168     public int getCodeSize()
169     {
170         return codeSize;
171     }
172 
173     /**
174      * This will determine the code size.
175      */
176     private void resetCodeSize()
177     {
178         if( nextCode >= 2048 )
179         {
180             codeSize = 12;
181         }
182         else if( nextCode >= 1024 )
183         {
184             codeSize = 11;
185         }
186         else if( nextCode >= 512 )
187         {
188             codeSize = 10;
189         }
190         else
191         {
192             codeSize = 9;
193         }
194     }
195 
196     /**
197      * This will crear the internal buffer that the dictionary uses.
198      */
199     public void clear()
200     {
201         buffer.reset();
202     }
203 
204     /**
205      * This will folow the path to the data node.
206      *
207      * @param data The path to the node.
208      *
209      * @return The node that resides at that path.
210      */
211     public LZWNode getNode( byte[] data )
212     {
213         return root.getNode( data );
214     }
215 }
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