src/proguard/classfile/editor/ConstantPoolSorter.java

/*
 * ProGuard -- shrinking, optimization, obfuscation, and preverification
 *             of Java bytecode.
 *
 * Copyright (c) 2002-2014 Eric Lafortune (eric@graphics.cornell.edu)
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the Free
 * Software Foundation; either version 2 of the License, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
 * more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */
package proguard.classfile.editor;

import proguard.classfile.*;
import proguard.classfile.constant.Constant;
import proguard.classfile.util.SimplifiedVisitor;
import proguard.classfile.visitor.ClassVisitor;

import java.util.Arrays;

/**
 * This ClassVisitor sorts the constant pool entries of the program classes
 * that it visits. The sorting order is based on the types of the constant pool
 * entries in the first place, and on their contents in the second place.
 *
 * @author Eric Lafortune
 */
public class ConstantPoolSorter
extends      SimplifiedVisitor
implements   ClassVisitor
{
    private int[]                constantIndexMap       = new int[ClassConstants.TYPICAL_CONSTANT_POOL_SIZE];
    private ComparableConstant[] comparableConstantPool = new ComparableConstant[ClassConstants.TYPICAL_CONSTANT_POOL_SIZE];
    private Constant[]           newConstantPool        = new Constant[ClassConstants.TYPICAL_CONSTANT_POOL_SIZE];

    private final ConstantPoolRemapper constantPoolRemapper = new ConstantPoolRemapper();


    // Implementations for ClassVisitor.

    public void visitProgramClass(ProgramClass programClass)
    {
        int constantPoolCount = programClass.u2constantPoolCount;

        // Sort the constant pool and set up an index map.
        if (constantIndexMap.length < constantPoolCount)
        {
            constantIndexMap       = new int[constantPoolCount];
            comparableConstantPool = new ComparableConstant[constantPoolCount];
            newConstantPool        = new Constant[constantPoolCount];
        }

        // Initialize an array whose elements can be compared.
        int sortLength = 0;
        for (int oldIndex = 1; oldIndex < constantPoolCount; oldIndex++)
        {
            Constant constant = programClass.constantPool[oldIndex];
            if (constant != null)
            {
                comparableConstantPool[sortLength++] =
                    new ComparableConstant(programClass, oldIndex, constant);
            }
        }

        // Sort the array.
        Arrays.sort(comparableConstantPool, 0, sortLength);

        // Save the sorted elements.
        int newLength = 1;
        int newIndex  = 1;
        ComparableConstant previousComparableConstant = null;
        for (int sortIndex = 0; sortIndex < sortLength; sortIndex++)
        {
            ComparableConstant comparableConstant = comparableConstantPool[sortIndex];

            // Isn't this a duplicate of the previous constant?
            if (!comparableConstant.equals(previousComparableConstant))
            {
                // Remember the index of the new entry.
                newIndex = newLength;

                // Copy the sorted constant pool entry over to the constant pool.
                Constant constant = comparableConstant.getConstant();

                newConstantPool[newLength++] = constant;

                // Long entries take up two slots, the second of which is null.
                int tag = constant.getTag();
                if (tag == ClassConstants.CONSTANT_Long ||
                    tag == ClassConstants.CONSTANT_Double)
                {
                    newConstantPool[newLength++] = null;
                }

                previousComparableConstant = comparableConstant;
            }

            // Fill out the map array.
            constantIndexMap[comparableConstant.getIndex()] = newIndex;
        }

        // Copy the new constant pool over.
        System.arraycopy(newConstantPool, 0, programClass.constantPool, 0, newLength);

        // Clear any remaining entries.
        Arrays.fill(programClass.constantPool, newLength, constantPoolCount, null);

        programClass.u2constantPoolCount = newLength;

        // Remap all constant pool references.
        constantPoolRemapper.setConstantIndexMap(constantIndexMap);
        constantPoolRemapper.visitProgramClass(programClass);
    }
}