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Java > Open Source Codes > org > apache > bcel > generic > SWITCH


1 /*
2  * Copyright 2000-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  *
16  */
17 package org.apache.bcel.generic;
18
19 /**
20  * SWITCH - Branch depending on int value, generates either LOOKUPSWITCH or
21  * TABLESWITCH instruction, depending on whether the match values (int[]) can be
22  * sorted with no gaps between the numbers.
23  *
24  * @version $Id: SWITCH.java 386056 2006-03-15 11:31:56Z tcurdt $
25  * @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
26  */
27 public final class SWITCH implements CompoundInstruction {
28
29     private int[] match;
30     private InstructionHandle[] targets;
31     private Select instruction;
32     private int match_length;
33
34
35     /**
36      * Template for switch() constructs. If the match array can be
37      * sorted in ascending order with gaps no larger than max_gap
38      * between the numbers, a TABLESWITCH instruction is generated, and
39      * a LOOKUPSWITCH otherwise. The former may be more efficient, but
40      * needs more space.
41      *
42      * Note, that the key array always will be sorted, though we leave
43      * the original arrays unaltered.
44      *
45      * @param match array of match values (case 2: ... case 7: ..., etc.)
46      * @param targets the instructions to be branched to for each case
47      * @param target the default target
48      * @param max_gap maximum gap that may between case branches
49      */
50     public SWITCH(int[] match, InstructionHandle[] targets, InstructionHandle target, int max_gap) {
51         this.match = (int[]) match.clone();
52         this.targets = (InstructionHandle[]) targets.clone();
53         if ((match_length = match.length) < 2) {
54             instruction = new TABLESWITCH(match, targets, target);
55         } else {
56             sort(0, match_length - 1);
57             if (matchIsOrdered(max_gap)) {
58                 fillup(max_gap, target);
59                 instruction = new TABLESWITCH(this.match, this.targets, target);
60             } else {
61                 instruction = new LOOKUPSWITCH(this.match, this.targets, target);
62             }
63         }
64     }
65
66
67     public SWITCH(int[] match, InstructionHandle[] targets, InstructionHandle target) {
68         this(match, targets, target, 1);
69     }
70
71
72     private final void fillup( int max_gap, InstructionHandle target ) {
73         int max_size = match_length + match_length * max_gap;
74         int[] m_vec = new int[max_size];
75         InstructionHandle[] t_vec = new InstructionHandle[max_size];
76         int count = 1;
77         m_vec[0] = match[0];
78         t_vec[0] = targets[0];
79         for (int i = 1; i < match_length; i++) {
80             int prev = match[i - 1];
81             int gap = match[i] - prev;
82             for (int j = 1; j < gap; j++) {
83                 m_vec[count] = prev + j;
84                 t_vec[count] = target;
85                 count++;
86             }
87             m_vec[count] = match[i];
88             t_vec[count] = targets[i];
89             count++;
90         }
91         match = new int[count];
92         targets = new InstructionHandle[count];
93         System.arraycopy(m_vec, 0, match, 0, count);
94         System.arraycopy(t_vec, 0, targets, 0, count);
95     }
96
97
98     /**
99      * Sort match and targets array with QuickSort.
100      */
101     private final void sort( int l, int r ) {
102         int i = l, j = r;
103         int h, m = match[(l + r) / 2];
104         InstructionHandle h2;
105         do {
106             while (match[i] < m) {
107                 i++;
108             }
109             while (m < match[j]) {
110                 j--;
111             }
112             if (i <= j) {
113                 h = match[i];
114                 match[i] = match[j];
115                 match[j] = h; // Swap elements
116 h2 = targets[i];
117                 targets[i] = targets[j];
118                 targets[j] = h2; // Swap instructions, too
119 i++;
120                 j--;
121             }
122         } while (i <= j);
123         if (l < j) {
124             sort(l, j);
125         }
126         if (i < r) {
127             sort(i, r);
128         }
129     }
130
131
132     /**
133      * @return match is sorted in ascending order with no gap bigger than max_gap?
134      */
135     private final boolean matchIsOrdered( int max_gap ) {
136         for (int i = 1; i < match_length; i++) {
137             if (match[i] - match[i - 1] > max_gap) {
138                 return false;
139             }
140         }
141         return true;
142     }
143
144
145     public final InstructionList getInstructionList() {
146         return new InstructionList(instruction);
147     }
148
149
150     public final Instruction getInstruction() {
151         return instruction;
152     }
153 }
154
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