branchinstruction.java

j2me 混淆包,用于混淆j2me的原代码用的

/* $Id: BranchInstruction.java,v 1.14 2004/10/10 20:56:58 eric Exp $
 *
 * ProGuard -- shrinking, optimization, and obfuscation of Java class files.
 *
 * Copyright (c) 2002-2004 Eric Lafortune ([e-mail])
 *
 * 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.instruction;

import proguard.classfile.*;
import proguard.classfile.attribute.*;

/**
 * This interface describes an instruction that branches to a given offset in
 * the code.
 *
 * @author Eric Lafortune
 */
public class BranchInstruction extends Instruction
{
    public int branchOffset;


    /**
     * Creates an uninitialized BranchInstruction.
     */
    public BranchInstruction() {}


    public BranchInstruction(byte opcode, int branchOffset)
    {
        this.opcode       = opcode;
        this.branchOffset = branchOffset;
    }


    /**
     * Copies the given instruction into this instruction.
     * @param branchInstruction the instruction to be copied.
     * @return this instruction.
     */
    public BranchInstruction copy(BranchInstruction branchInstruction)
    {
        this.opcode       = branchInstruction.opcode;
        this.branchOffset = branchInstruction.branchOffset;

        return this;
    }


    // Implementations for Instruction.

    public Instruction shrink()
    {
        // Is this a wide branch that can be replaced by a normal branch?
        if (branchOffset << 16 >> 16 == branchOffset)
        {
            if      (opcode == InstructionConstants.OP_GOTO_W)
            {
                opcode = InstructionConstants.OP_GOTO;
            }
            else if (opcode == InstructionConstants.OP_JSR_W)
            {
                opcode = InstructionConstants.OP_JSR;
            }
        }

        return this;
    }

    protected void readInfo(byte[] code, int offset)
    {
        branchOffset = readSignedValue(code, offset, branchOffsetSize());
    }


    protected void writeInfo(byte[] code, int offset)
    {
        writeValue(code, offset, branchOffset, branchOffsetSize());
    }


    public int length(int offset)
    {
        return 1 + branchOffsetSize();
    }


    public void accept(ClassFile classFile, MethodInfo methodInfo, CodeAttrInfo codeAttrInfo, int offset, InstructionVisitor instructionVisitor)
    {
        instructionVisitor.visitBranchInstruction(classFile, methodInfo, codeAttrInfo, offset, this);
    }


    public String toString(int offset)
    {
        return "["+offset+"] "+getName()+" (offset="+branchOffset+", target="+(offset+branchOffset)+")";
    }


    // Implementations for Object.

    public String toString()
    {
        return getName()+" (offset="+branchOffset+")";
    }


    // Small utility methods.

    /**
     * Computes the appropriate branch offset size for this instruction.
     */
    private int branchOffsetSize()
    {
        return opcode == InstructionConstants.OP_GOTO_W ||
               opcode == InstructionConstants.OP_JSR_W  ? 4 :
                                                          2;
    }
}