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/*
* 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.instruction;
import proguard.classfile.*;
import proguard.classfile.attribute.CodeAttribute;
import proguard.classfile.instruction.visitor.InstructionVisitor;
/**
* 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 byte canonicalOpcode()
{
// Remove the _w extension, if any.
switch (opcode)
{
case InstructionConstants.OP_GOTO_W: return InstructionConstants.OP_GOTO;
case InstructionConstants.OP_JSR_W: return InstructionConstants.OP_JSR;
default: return opcode;
}
}
public Instruction shrink()
{
// Do we need an ordinary branch or a wide branch?
if (requiredBranchOffsetSize() == 2)
{
// Can we replace the wide branch by an ordinary branch?
if (opcode == InstructionConstants.OP_GOTO_W)
{
opcode = InstructionConstants.OP_GOTO;
}
else if (opcode == InstructionConstants.OP_JSR_W)
{
opcode = InstructionConstants.OP_JSR;
}
}
else
{
// Should we replace the ordinary branch by a wide branch?
if (opcode == InstructionConstants.OP_GOTO)
{
opcode = InstructionConstants.OP_GOTO_W;
}
else if (opcode == InstructionConstants.OP_JSR)
{
opcode = InstructionConstants.OP_JSR_W;
}
else
{
throw new IllegalArgumentException("Branch instruction can't be widened ("+this.toString()+")");
}
}
return this;
}
protected void readInfo(byte[] code, int offset)
{
branchOffset = readSignedValue(code, offset, branchOffsetSize());
}
protected void writeInfo(byte[] code, int offset)
{
if (requiredBranchOffsetSize() > branchOffsetSize())
{
throw new IllegalArgumentException("Instruction has invalid branch offset size ("+this.toString(offset)+")");
}
writeSignedValue(code, offset, branchOffset, branchOffsetSize());
}
public int length(int offset)
{
return 1 + branchOffsetSize();
}
public void accept(Clazz clazz, Method method, CodeAttribute codeAttribute, int offset, InstructionVisitor instructionVisitor)
{
instructionVisitor.visitBranchInstruction(clazz, method, codeAttribute, offset, this);
}
public String toString(int offset)
{
return "["+offset+"] "+toString()+" (target="+(offset+branchOffset)+")";
}
// Implementations for Object.
public String toString()
{
return getName()+" "+(branchOffset >= 0 ? "+" : "")+branchOffset;
}
// Small utility methods.
/**
* Returns the branch offset size for this instruction.
*/
private int branchOffsetSize()
{
return opcode == InstructionConstants.OP_GOTO_W ||
opcode == InstructionConstants.OP_JSR_W ? 4 :
2;
}
/**
* Computes the required branch offset size for this instruction's branch
* offset.
*/
private int requiredBranchOffsetSize()
{
return (short)branchOffset == branchOffset ? 2 : 4;
}
}
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