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Java > Open Source Codes > proguard > obfuscate > NameAndTypeShrinker


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.attribute.*;
25 import proguard.classfile.constant.Constant;
26 import proguard.classfile.editor.ConstantPoolRemapper;
27 import proguard.classfile.instruction.*;
28 import proguard.classfile.visitor.*;
29
30
31 /**
32  * This ClassVisitor removes NameAndType constant pool entries
33  * that are not marked as being used.
34  *
35  * @see NameAndTypeUsageMarker
36  *
37  * @author Eric Lafortune
38  */
39 public class NameAndTypeShrinker implements ClassVisitor
40 {
41     private int[] constantIndexMap;
42     private ConstantPoolRemapper constantPoolRemapper = new ConstantPoolRemapper();
43
44
45     // Implementations for ClassVisitor.
46
47     public void visitProgramClass(ProgramClass programClass)
48     {
49         // Shift the used constant pool entries together, filling out the
50 // index map.
51 programClass.u2constantPoolCount =
52             shrinkConstantPool(programClass.constantPool,
53                                programClass.u2constantPoolCount);
54
55
56         // Remap all constant pool references.
57 constantPoolRemapper.setConstantIndexMap(constantIndexMap);
58         constantPoolRemapper.visitProgramClass(programClass);
59     }
60
61
62     public void visitLibraryClass(LibraryClass libraryClass)
63     {
64     }
65
66
67     // Small utility methods.
68
69     /**
70      * Removes all NameAndType entries that are not marked as being used
71      * from the given constant pool.
72      * @return the new number of entries.
73      */
74     private int shrinkConstantPool(Constant[] constantPool, int length)
75     {
76         // Create a new index map, if necessary.
77 if (constantIndexMap == null ||
78             constantIndexMap.length < length)
79         {
80             constantIndexMap = new int[length];
81         }
82
83         int counter = 1;
84         boolean isUsed = false;
85
86         // Shift the used constant pool entries together.
87 for (int index = 1; index < length; index++)
88         {
89             constantIndexMap[index] = counter;
90
91             Constant constant = constantPool[index];
92
93             // Don't update the flag if this is the second half of a long entry.
94 if (constant != null)
95             {
96                 isUsed = constant.getTag() != ClassConstants.CONSTANT_NameAndType ||
97                          NameAndTypeUsageMarker.isUsed(constant);
98             }
99
100             if (isUsed)
101             {
102                 constantPool[counter++] = constant;
103             }
104         }
105
106         // Clear the remaining constant pool elements.
107 for (int index = counter; index < length; index++)
108         {
109             constantPool[index] = null;
110         }
111
112         return counter;
113     }
114 }
115
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