1   package org.apache.bcel.generic;
2   
3   /* ====================================================================
4    * The Apache Software License, Version 1.1
5    *
6    * Copyright (c) 2001 The Apache Software Foundation.  All rights
7    * reserved.
8    *
9    * Redistribution and use in source and binary forms, with or without
10   * modification, are permitted provided that the following conditions
11   * are met:
12   *
13   * 1. Redistributions of source code must retain the above copyright
14   *    notice, this list of conditions and the following disclaimer.
15   *
16   * 2. Redistributions in binary form must reproduce the above copyright
17   *    notice, this list of conditions and the following disclaimer in
18   *    the documentation and/or other materials provided with the
19   *    distribution.
20   *
21   * 3. The end-user documentation included with the redistribution,
22   *    if any, must include the following acknowledgment:
23   *       "This product includes software developed by the
24   *        Apache Software Foundation (http://www.apache.org/)."
25   *    Alternately, this acknowledgment may appear in the software itself,
26   *    if and wherever such third-party acknowledgments normally appear.
27   *
28   * 4. The names "Apache" and "Apache Software Foundation" and
29   *    "Apache BCEL" must not be used to endorse or promote products
30   *    derived from this software without prior written permission. For
31   *    written permission, please contact apache@apache.org.
32   *
33   * 5. Products derived from this software may not be called "Apache",
34   *    "Apache BCEL", nor may "Apache" appear in their name, without
35   *    prior written permission of the Apache Software Foundation.
36   *
37   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
38   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
39   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40   * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
41   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
42   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
43   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
44   * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
45   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48   * SUCH DAMAGE.
49   * ====================================================================
50   *
51   * This software consists of voluntary contributions made by many
52   * individuals on behalf of the Apache Software Foundation.  For more
53   * information on the Apache Software Foundation, please see
54   * <http://www.apache.org/>.
55   */
56  
57  import java.io.*;
58  import org.apache.bcel.util.ByteSequence;
59  
60  /*** 
61   * Abstract super class for branching instructions like GOTO, IFEQ, etc..
62   * Branch instructions may have a variable length, namely GOTO, JSR, 
63   * LOOKUPSWITCH and TABLESWITCH.
64   *
65   * @see InstructionList
66   * @version $Id: BranchInstruction.java,v 1.1.1.1 2001/10/29 20:00:07 jvanzyl Exp $
67   * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
68   */
69  public abstract class BranchInstruction extends Instruction implements InstructionTargeter {
70    protected int               index;    // Branch target relative to this instruction
71    protected InstructionHandle target;   // Target object in instruction list
72    protected int               position; // Byte code offset
73  
74    /***
75     * Empty constructor needed for the Class.newInstance() statement in
76     * Instruction.readInstruction(). Not to be used otherwise.
77     */
78    BranchInstruction() {}
79  
80    /*** Common super constructor
81     * @param opcodee Instruction opcode
82     * @param target instruction to branch to
83     */
84    protected BranchInstruction(short opcode, InstructionHandle target) {
85      super(opcode, (short)3);
86      setTarget(target);
87    }
88  
89    /***
90     * Dump instruction as byte code to stream out.
91     * @param out Output stream
92     */
93    public void dump(DataOutputStream out) throws IOException {
94      out.writeByte(opcode);
95  
96      index = getTargetOffset();
97  
98      if(Math.abs(index) >= 32767) // too large for short
99        throw new ClassGenException("Branch target offset too large for short");
100 
101     out.writeShort(index); // May be negative, i.e., point backwards
102   }
103 
104   /***
105    * @param target branch target
106    * @return the offset to  `target' relative to this instruction
107    */
108   protected int getTargetOffset(InstructionHandle target) {
109     if(target == null)
110       throw new ClassGenException("Target of " + super.toString(true) + 
111 				  " is invalid null handle");
112 
113     int t = target.getPosition();
114 
115     if(t < 0)
116       throw new ClassGenException("Invalid branch target position offset for " +
117 				  super.toString(true) + ":" + t + ":" + target);
118 
119     return t - position;
120   }
121 
122   /***
123    * @return the offset to this instruction's target
124    */
125   protected int getTargetOffset() { return getTargetOffset(target); }
126 
127   /***
128    * Called by InstructionList.setPositions when setting the position for every
129    * instruction. In the presence of variable length instructions `setPositions'
130    * performs multiple passes over the instruction list to calculate the
131    * correct (byte) positions and offsets by calling this function.
132    *
133    * @param offset additional offset caused by preceding (variable length) instructions
134    * @param max_offset the maximum offset that may be caused by these instructions
135    * @return additional offset caused by possible change of this instruction's length
136    */
137   protected int updatePosition(int offset, int max_offset) {
138     position += offset;
139     return 0;
140   }
141 
142   /***
143    * Long output format:
144    *
145    * <position in byte code>
146    * <name of opcode> "["<opcode number>"]" 
147    * "("<length of instruction>")"
148    * "<"<target instruction>">" "@"<branch target offset>
149    *
150    * @param verbose long/short format switch
151    * @return mnemonic for instruction
152    */
153   public String toString(boolean verbose) {
154     String s = super.toString(verbose);
155     String t = "null";
156 
157     if(verbose) {
158       if(target != null) {
159 	if(target.getInstruction() == this)
160 	  t = "<points to itself>";
161 	else if(target.getInstruction() == null)
162 	  t = "<null instruction!!!?>";
163 	else
164 	  t = target.getInstruction().toString(false); // Avoid circles
165       }
166     } else {
167       if(target != null) {
168 	index = getTargetOffset();
169 	t = "" + (index + position);
170       }
171     }
172 
173     return s + " -> " + t;
174   }
175 
176   /***
177    * Read needed data (e.g. index) from file. Conversion to a InstructionHandle
178    * is done in InstructionList(byte[]).
179    *
180    * @param bytes input stream
181    * @param wide wide prefix?
182    * @see InstructionList
183    */
184   protected void initFromFile(ByteSequence bytes, boolean wide) throws IOException
185   {
186     length = 3;
187     index  = bytes.readShort();
188   }
189 
190   /***
191    * @return target offset in byte code
192    */
193   public final int getIndex() { return index; }
194 
195   /***
196    * @return target of branch instruction
197    */
198   public InstructionHandle getTarget() { return target; }
199 
200   /***
201    * Set branch target
202    * @param target branch target
203    */
204   public void setTarget(InstructionHandle target) {
205     notifyTarget(this.target, target, this);
206     this.target = target;
207   }
208 
209   /***
210    * Used by BranchInstruction, LocalVariableGen, CodeExceptionGen
211    */
212   static final void notifyTarget(InstructionHandle old_ih, InstructionHandle new_ih,
213 				 InstructionTargeter t) {
214     if(old_ih != null)
215       old_ih.removeTargeter(t);
216     if(new_ih != null)
217       new_ih.addTargeter(t);
218   }
219 
220   /***
221    * @param old_ih old target
222    * @param new_ih new target
223    */
224   public void updateTarget(InstructionHandle old_ih, InstructionHandle new_ih) {
225     if(target == old_ih)
226       setTarget(new_ih);
227     else
228       throw new ClassGenException("Not targeting " + old_ih + ", but " + target);
229   }
230 
231   /***
232    * @return true, if ih is target of this instruction
233    */
234   public boolean containsTarget(InstructionHandle ih) {
235     return (target == ih);
236   }
237 
238   /***
239    * Inform target that it's not targeted anymore.
240    */
241   void dispose() {
242     setTarget(null);
243     index=-1;
244     position=-1;
245   }
246 }
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