1 /*
   2  * reserved comment block
   3  * DO NOT REMOVE OR ALTER!
   4  */
   5 package com.sun.org.apache.bcel.internal.generic;
   6 
   7 /* ====================================================================
   8  * The Apache Software License, Version 1.1
   9  *
  10  * Copyright (c) 2001 The Apache Software Foundation.  All rights
  11  * reserved.
  12  *
  13  * Redistribution and use in source and binary forms, with or without
  14  * modification, are permitted provided that the following conditions
  15  * are met:
  16  *
  17  * 1. Redistributions of source code must retain the above copyright
  18  *    notice, this list of conditions and the following disclaimer.
  19  *
  20  * 2. Redistributions in binary form must reproduce the above copyright
  21  *    notice, this list of conditions and the following disclaimer in
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  23  *    distribution.
  24  *
  25  * 3. The end-user documentation included with the redistribution,
  26  *    if any, must include the following acknowledgment:
  27  *       "This product includes software developed by the
  28  *        Apache Software Foundation (http://www.apache.org/)."
  29  *    Alternately, this acknowledgment may appear in the software itself,
  30  *    if and wherever such third-party acknowledgments normally appear.
  31  *
  32  * 4. The names "Apache" and "Apache Software Foundation" and
  33  *    "Apache BCEL" must not be used to endorse or promote products
  34  *    derived from this software without prior written permission. For
  35  *    written permission, please contact apache@apache.org.
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  37  * 5. Products derived from this software may not be called "Apache",
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  55  * This software consists of voluntary contributions made by many
  56  * individuals on behalf of the Apache Software Foundation.  For more
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  59  */
  60 
  61 import java.io.*;
  62 import com.sun.org.apache.bcel.internal.util.ByteSequence;
  63 
  64 /**
  65  * Abstract super class for branching instructions like GOTO, IFEQ, etc..
  66  * Branch instructions may have a variable length, namely GOTO, JSR,
  67  * LOOKUPSWITCH and TABLESWITCH.
  68  *
  69  * @see InstructionList
  70  * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
  71  */
  72 public abstract class BranchInstruction extends Instruction implements InstructionTargeter {
  73   protected int               index;    // Branch target relative to this instruction
  74   protected InstructionHandle target;   // Target object in instruction list
  75   protected int               position; // Byte code offset
  76 
  77   /**
  78    * Empty constructor needed for the Class.newInstance() statement in
  79    * Instruction.readInstruction(). Not to be used otherwise.
  80    */
  81   BranchInstruction() {}
  82 
  83   /** Common super constructor
  84    * @param opcodee Instruction opcode
  85    * @param target instruction to branch to
  86    */
  87   protected BranchInstruction(short opcode, InstructionHandle target) {
  88     super(opcode, (short)3);
  89     setTarget(target);
  90   }
  91 
  92   /**
  93    * Dump instruction as byte code to stream out.
  94    * @param out Output stream
  95    */
  96   public void dump(DataOutputStream out) throws IOException {
  97     out.writeByte(opcode);
  98 
  99     index = getTargetOffset();
 100 
 101     if(Math.abs(index) >= 32767) // too large for short
 102       throw new ClassGenException("Branch target offset too large for short");
 103 
 104     out.writeShort(index); // May be negative, i.e., point backwards
 105   }
 106 
 107   /**
 108    * @param target branch target
 109    * @return the offset to  `target' relative to this instruction
 110    */
 111   protected int getTargetOffset(InstructionHandle target) {
 112     if(target == null)
 113       throw new ClassGenException("Target of " + super.toString(true) +
 114                                   " is invalid null handle");
 115 
 116     int t = target.getPosition();
 117 
 118     if(t < 0)
 119       throw new ClassGenException("Invalid branch target position offset for " +
 120                                   super.toString(true) + ":" + t + ":" + target);
 121 
 122     return t - position;
 123   }
 124 
 125   /**
 126    * @return the offset to this instruction's target
 127    */
 128   protected int getTargetOffset() { return getTargetOffset(target); }
 129 
 130   /**
 131    * Called by InstructionList.setPositions when setting the position for every
 132    * instruction. In the presence of variable length instructions `setPositions'
 133    * performs multiple passes over the instruction list to calculate the
 134    * correct (byte) positions and offsets by calling this function.
 135    *
 136    * @param offset additional offset caused by preceding (variable length) instructions
 137    * @param max_offset the maximum offset that may be caused by these instructions
 138    * @return additional offset caused by possible change of this instruction's length
 139    */
 140   protected int updatePosition(int offset, int max_offset) {
 141     position += offset;
 142     return 0;
 143   }
 144 
 145   /**
 146    * Long output format:
 147    *
 148    * &lt;position in byte code&gt;
 149    * &lt;name of opcode&gt; "["&lt;opcode number&gt;"]"
 150    * "("&lt;length of instruction&gt;")"
 151    * "&lt;"&lt;target instruction&gt;"&gt;" "@"&lt;branch target offset&gt;
 152    *
 153    * @param verbose long/short format switch
 154    * @return mnemonic for instruction
 155    */
 156   public String toString(boolean verbose) {
 157     String s = super.toString(verbose);
 158     String t = "null";
 159 
 160     if(verbose) {
 161       if(target != null) {
 162         if(target.getInstruction() == this)
 163           t = "<points to itself>";
 164         else if(target.getInstruction() == null)
 165           t = "<null instruction!!!?>";
 166         else
 167           t = target.getInstruction().toString(false); // Avoid circles
 168       }
 169     } else {
 170       if(target != null) {
 171         index = getTargetOffset();
 172         t = "" + (index + position);
 173       }
 174     }
 175 
 176     return s + " -> " + t;
 177   }
 178 
 179   /**
 180    * Read needed data (e.g. index) from file. Conversion to a InstructionHandle
 181    * is done in InstructionList(byte[]).
 182    *
 183    * @param bytes input stream
 184    * @param wide wide prefix?
 185    * @see InstructionList
 186    */
 187   protected void initFromFile(ByteSequence bytes, boolean wide) throws IOException
 188   {
 189     length = 3;
 190     index  = bytes.readShort();
 191   }
 192 
 193   /**
 194    * @return target offset in byte code
 195    */
 196   public final int getIndex() { return index; }
 197 
 198   /**
 199    * @return target of branch instruction
 200    */
 201   public InstructionHandle getTarget() { return target; }
 202 
 203   /**
 204    * Set branch target
 205    * @param target branch target
 206    */
 207   public void setTarget(InstructionHandle target) {
 208     notifyTarget(this.target, target, this);
 209     this.target = target;
 210   }
 211 
 212   /**
 213    * Used by BranchInstruction, LocalVariableGen, CodeExceptionGen
 214    */
 215   static final void notifyTarget(InstructionHandle old_ih, InstructionHandle new_ih,
 216                                  InstructionTargeter t) {
 217     if(old_ih != null)
 218       old_ih.removeTargeter(t);
 219     if(new_ih != null)
 220       new_ih.addTargeter(t);
 221   }
 222 
 223   /**
 224    * @param old_ih old target
 225    * @param new_ih new target
 226    */
 227   public void updateTarget(InstructionHandle old_ih, InstructionHandle new_ih) {
 228     if(target == old_ih)
 229       setTarget(new_ih);
 230     else
 231       throw new ClassGenException("Not targeting " + old_ih + ", but " + target);
 232   }
 233 
 234   /**
 235    * @return true, if ih is target of this instruction
 236    */
 237   public boolean containsTarget(InstructionHandle ih) {
 238     return (target == ih);
 239   }
 240 
 241   /**
 242    * Inform target that it's not targeted anymore.
 243    */
 244   void dispose() {
 245     setTarget(null);
 246     index=-1;
 247     position=-1;
 248   }
 249 }