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.
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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.
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16   * 2. Redistributions in binary form must reproduce the above copyright
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22   *    if any, must include the following acknowledgment:
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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.
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50   *
51   * This software consists of voluntary contributions made by many
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55   */
56  
57  /*** 
58   * SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or
59   * TABLESWITCH instruction, depending on whether the match values (int[]) can be
60   * sorted with no gaps between the numbers.
61   *
62   * @version $Id: SWITCH.java,v 1.1.1.1 2001/10/29 20:00:27 jvanzyl Exp $
63   * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
64   */
65  public final class SWITCH implements CompoundInstruction {
66    private int[]               match;
67    private InstructionHandle[] targets;
68    private Select              instruction;
69    private int                 match_length;
70  
71    /***
72     * Template for switch() constructs. If the match array can be
73     * sorted in ascending order with gaps no larger than max_gap
74     * between the numbers, a TABLESWITCH instruction is generated, and
75     * a LOOKUPSWITCH otherwise. The former may be more efficient, but
76     * needs more space.
77     * 
78     * Note, that the key array always will be sorted, though we leave
79     * the original arrays unaltered.
80     *
81     * @param match array of match values (case 2: ... case 7: ..., etc.)
82     * @param targets the instructions to be branched to for each case
83     * @param target the default target
84     * @param max_gap maximum gap that may between case branches
85     */
86    public SWITCH(int[] match, InstructionHandle[] targets,
87  		InstructionHandle target, int max_gap) {
88      this.match   = (int[])match.clone();
89      this.targets = (InstructionHandle[])targets.clone();
90  
91      if((match_length = match.length) < 2) // (almost) empty switch, or just default
92        instruction = new TABLESWITCH(match, targets, target);
93      else {
94        sort(0, match_length - 1);
95        
96        if(matchIsOrdered(max_gap)) {
97  	fillup(max_gap, target);
98  
99  	instruction = new TABLESWITCH(this.match, this.targets, target);
100       }
101       else
102 	instruction = new LOOKUPSWITCH(this.match, this.targets, target);
103     }
104   }
105 
106   public SWITCH(int[] match, InstructionHandle[] targets,
107 		InstructionHandle target) {
108     this(match, targets, target, 1);
109   }
110   
111   private final void fillup(int max_gap, InstructionHandle target) {
112     int                 max_size = match_length + match_length * max_gap;
113     int[]               m_vec    = new int[max_size];
114     InstructionHandle[] t_vec    = new InstructionHandle[max_size];
115     int                 count    = 1;
116 
117     m_vec[0] = match[0];
118     t_vec[0] = targets[0];
119 
120     for(int i=1; i < match_length; i++) {
121       int prev = match[i-1];
122       int gap  = match[i] - prev; 
123 
124       for(int j=1; j < gap; j++) {
125 	m_vec[count] = prev + j;
126 	t_vec[count] = target;
127 	count++;
128       }
129 
130       m_vec[count] = match[i];
131       t_vec[count] = targets[i];
132       count++;
133     }	
134 
135     match   = new int[count];
136     targets = new InstructionHandle[count];
137 
138     System.arraycopy(m_vec, 0, match, 0, count);
139     System.arraycopy(t_vec, 0, targets, 0, count);
140   }
141 
142   /***
143    * Sort match and targets array with QuickSort.
144    */
145   private final void sort(int l, int r) {
146     int i = l, j = r;
147     int h, m = match[(l + r) / 2];
148     InstructionHandle h2;
149 
150     do {
151       while(match[i] < m) i++;
152       while(m < match[j]) j--;
153 
154       if(i <= j) {
155 	h=match[i]; match[i]=match[j]; match[j]=h; // Swap elements
156 	h2=targets[i]; targets[i]=targets[j]; targets[j]=h2; // Swap instructions, too
157 	i++; j--;
158       }
159     } while(i <= j);
160 
161     if(l < j) sort(l, j);
162     if(i < r) sort(i, r);
163   }
164 
165   /***
166    * @return match is sorted in ascending order with no gap bigger than max_gap?
167    */
168   private final boolean matchIsOrdered(int max_gap) {
169     for(int i=1; i < match_length; i++)
170       if(match[i] - match[i-1] > max_gap)
171 	return false;
172 
173     return true;
174   }
175 
176   public final InstructionList getInstructionList() {
177     return new InstructionList(instruction);
178   }
179 
180   public final Instruction getInstruction() {
181     return instruction;
182   }
183 }
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