/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package org.apache.bcel.generic;
import java.io.DataOutputStream;
import java.io.IOException;
import org.apache.bcel.util.ByteSequence;
/**
* Abstract super class for branching instructions like GOTO, IFEQ, etc..
* Branch instructions may have a variable length, namely GOTO, JSR,
* LOOKUPSWITCH and TABLESWITCH.
*
* @see InstructionList
* @version $Id: BranchInstruction.java 1589401 2014-04-23 12:56:36Z ebourg $
* @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
*/
public abstract class BranchInstruction extends Instruction implements InstructionTargeter {
private static final long serialVersionUID = 3225905281842405051L;
protected int index; // Branch target relative to this instruction
protected InstructionHandle target; // Target object in instruction list
protected int position; // Byte code offset
/**
* Empty constructor needed for the Class.newInstance() statement in
* Instruction.readInstruction(). Not to be used otherwise.
*/
BranchInstruction() {
}
/** Common super constructor
* @param opcode Instruction opcode
* @param target instruction to branch to
*/
protected BranchInstruction(short opcode, InstructionHandle target) {
super(opcode, (short) 3);
setTarget(target);
}
/**
* Dump instruction as byte code to stream out.
* @param out Output stream
*/
@Override
public void dump( DataOutputStream out ) throws IOException {
out.writeByte(opcode);
index = getTargetOffset();
if (Math.abs(index) >= 32767) {
throw new ClassGenException("Branch target offset too large for short: " + index);
}
out.writeShort(index); // May be negative, i.e., point backwards
}
/**
* @param _target branch target
* @return the offset to `target' relative to this instruction
*/
protected int getTargetOffset( InstructionHandle _target ) {
if (_target == null) {
throw new ClassGenException("Target of " + super.toString(true)
+ " is invalid null handle");
}
int t = _target.getPosition();
if (t < 0) {
throw new ClassGenException("Invalid branch target position offset for "
+ super.toString(true) + ":" + t + ":" + _target);
}
return t - position;
}
/**
* @return the offset to this instruction's target
*/
protected int getTargetOffset() {
return getTargetOffset(target);
}
/**
* Called by InstructionList.setPositions when setting the position for every
* instruction. In the presence of variable length instructions `setPositions'
* performs multiple passes over the instruction list to calculate the
* correct (byte) positions and offsets by calling this function.
*
* @param offset additional offset caused by preceding (variable length) instructions
* @param max_offset the maximum offset that may be caused by these instructions
* @return additional offset caused by possible change of this instruction's length
*/
protected int updatePosition( int offset, int max_offset ) {
position += offset;
return 0;
}
/**
* Long output format:
*
* <position in byte code>
* <name of opcode> "["<opcode number>"]"
* "("<length of instruction>")"
* "<"<target instruction>">" "@"<branch target offset>
*
* @param verbose long/short format switch
* @return mnemonic for instruction
*/
@Override
public String toString( boolean verbose ) {
String s = super.toString(verbose);
String t = "null";
if (verbose) {
if (target != null) {
if (target.getInstruction() == this) {
t = "<points to itself>";
} else if (target.getInstruction() == null) {
t = "<null instruction!!!?>";
} else {
t = target.getInstruction().toString(false); // Avoid circles
}
}
} else {
if (target != null) {
index = getTargetOffset();
t = "" + (index + position);
}
}
return s + " -> " + t;
}
/**
* Read needed data (e.g. index) from file. Conversion to a InstructionHandle
* is done in InstructionList(byte[]).
*
* @param bytes input stream
* @param wide wide prefix?
* @see InstructionList
*/
@Override
protected void initFromFile( ByteSequence bytes, boolean wide ) throws IOException {
length = 3;
index = bytes.readShort();
}
/**
* @return target offset in byte code
*/
public final int getIndex() {
return index;
}
/**
* @return target of branch instruction
*/
public InstructionHandle getTarget() {
return target;
}
/**
* Set branch target
* @param target branch target
*/
public void setTarget( InstructionHandle target ) {
notifyTarget(this.target, target, this);
this.target = target;
}
/**
* Used by BranchInstruction, LocalVariableGen, CodeExceptionGen
*/
static void notifyTarget( InstructionHandle old_ih, InstructionHandle new_ih,
InstructionTargeter t ) {
if (old_ih != null) {
old_ih.removeTargeter(t);
}
if (new_ih != null) {
new_ih.addTargeter(t);
}
}
/**
* @param old_ih old target
* @param new_ih new target
*/
public void updateTarget( InstructionHandle old_ih, InstructionHandle new_ih ) {
if (target == old_ih) {
setTarget(new_ih);
} else {
throw new ClassGenException("Not targeting " + old_ih + ", but " + target);
}
}
/**
* @return true, if ih is target of this instruction
*/
public boolean containsTarget( InstructionHandle ih ) {
return (target == ih);
}
/**
* Inform target that it's not targeted anymore.
*/
@Override
void dispose() {
setTarget(null);
index = -1;
position = -1;
}
}