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Java > Open Source Codes > com > sun > org > apache > bcel > internal > generic > SWITCH


1 package com.sun.org.apache.bcel.internal.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:
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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
17  * notice, this list of conditions and the following disclaimer in
18  * the documentation and/or other materials provided with the
19  * distribution.
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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
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34  * "Apache BCEL", nor may "Apache" appear in their name, without
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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 }
184
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