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      1 /*
      2  * ProGuard -- shrinking, optimization, obfuscation, and preverification
      3  *             of Java bytecode.
      4  *
      5  * Copyright (c) 2002-2009 Eric Lafortune (eric (at) 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 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