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Java > Open Source Codes > proguard > obfuscate > Utf8Shrinker


1 /*
2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
3  * of Java bytecode.
4  *
5  * Copyright (c) 2002-2007 Eric Lafortune (eric@graphics.cornell.edu)
6  *
7  * This program is free software; you can redistribute it and/or modify it
8  * under the terms of the GNU General Public License as published by the Free
9  * Software Foundation; either version 2 of the License, or (at your option)
10  * any later version.
11  *
12  * This program is distributed in the hope that it will be useful, but WITHOUT
13  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
15  * more details.
16  *
17  * You should have received a copy of the GNU General Public License along
18  * with this program; if not, write to the Free Software Foundation, Inc.,
19  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
20  */
21 package proguard.obfuscate;
22
23 import proguard.classfile.*;
24 import proguard.classfile.constant.Constant;
25 import proguard.classfile.editor.ConstantPoolRemapper;
26 import proguard.classfile.visitor.ClassVisitor;
27
28
29 /**
30  * This ClassVisitor removes UTF-8 constant pool entries that are not marked
31  * as being used.
32  *
33  * @see Utf8UsageMarker
34  *
35  * @author Eric Lafortune
36  */
37 public class Utf8Shrinker implements ClassVisitor
38 {
39     private int[] constantIndexMap = new int[ClassConstants.TYPICAL_CONSTANT_POOL_SIZE];
40     private ConstantPoolRemapper constantPoolRemapper = new ConstantPoolRemapper();
41
42
43     // Implementations for ClassVisitor.
44
45     public void visitProgramClass(ProgramClass programClass)
46     {
47         // Shift the used constant pool entries together, filling out the
48 // index map.
49 programClass.u2constantPoolCount =
50             shrinkConstantPool(programClass.constantPool,
51                                programClass.u2constantPoolCount);
52
53         // Remap all constant pool references.
54 constantPoolRemapper.setConstantIndexMap(constantIndexMap);
55         constantPoolRemapper.visitProgramClass(programClass);
56     }
57
58
59     public void visitLibraryClass(LibraryClass libraryClass)
60     {
61     }
62
63
64     // Small utility methods.
65
66     /**
67      * Removes all UTF-8 entries that are not marked as being used
68      * from the given constant pool.
69      * @return the new number of entries.
70      */
71     private int shrinkConstantPool(Constant[] constantPool, int length)
72     {
73         // Create a new index map, if necessary.
74 if (constantIndexMap.length < length)
75         {
76             constantIndexMap = new int[length];
77         }
78
79         int counter = 1;
80         boolean isUsed = false;
81
82         // Shift the used constant pool entries together.
83 for (int index = 1; index < length; index++)
84         {
85             constantIndexMap[index] = counter;
86
87             Constant constant = constantPool[index];
88
89             // Don't update the flag if this is the second half of a long entry.
90 if (constant != null)
91             {
92                 isUsed = constant.getTag() != ClassConstants.CONSTANT_Utf8 ||
93                          Utf8UsageMarker.isUsed(constant);
94             }
95
96             if (isUsed)
97             {
98                 constantPool[counter++] = constant;
99             }
100         }
101
102         // Clear the remaining constant pool elements.
103 for (int index = counter; index < length; index++)
104         {
105             constantPool[index] = null;
106         }
107
108         return counter;
109     }
110 }
111
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