1/*
2 * ProGuard -- shrinking, optimization, obfuscation, and preverification
3 *             of Java bytecode.
4 *
5 * Copyright (c) 2002-2009 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 */
21package proguard.obfuscate;
22
23import proguard.classfile.*;
24import proguard.classfile.constant.Constant;
25import proguard.classfile.editor.ConstantPoolRemapper;
26import 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 */
37public class Utf8Shrinker implements ClassVisitor
38{
39    private int[]                constantIndexMap     = new int[ClassConstants.TYPICAL_CONSTANT_POOL_SIZE];
40    private final 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