package com.sun.org.apache.bcel.internal.generic;
/* ====================================================================
* The Apache Software License, Version 1.1
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*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
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*/
import java.io.*;
import com.sun.org.apache.bcel.internal.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,v 1.1.2.1 2005/07/31 23:45:32 jeffsuttor Exp $
* @author <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
*/
public abstract class BranchInstruction extends Instruction implements InstructionTargeter {
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 opcodee 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
*/
public void dump(DataOutputStream out) throws IOException {
out.writeByte(opcode);
index = getTargetOffset();
if(Math.abs(index) >= 32767) // too large for short
throw new ClassGenException("Branch target offset too large for short");
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
*/
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
*/
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 final 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.
*/
void dispose() {
setTarget(null);
index=-1;
position=-1;
}
}
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