1 /*******************************************************************************
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
3 *
4 * All rights reserved. This program and the accompanying materials
5 * are made available under the terms of the Eclipse Public License v1.0
6 * which accompanies this distribution, and is available at
7 * http://www.eclipse.org/legal/epl-v10.html
8 *
9 * Alternatively, the contents of this file may be used under the terms of
10 * either the GNU Lesser General Public License Version 2.1 or later (the
11 * "LGPL"), in which case the provisions of the LGPL are applicable instead
12 * of those above. If you wish to allow use of your version of this file only
13 * under the terms of the LGPL, and not to allow others to use your version of
14 * this file under the terms of the EPL, indicate your decision by deleting
15 * the provisions above and replace them with the notice and other provisions
16 * required by the LGPL. If you do not delete the provisions above, a recipient
17 * may use your version of this file under the terms of the EPL or the LGPL.
18 *
19 * Based on the original MiniSat specification from:
20 *
21 * An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
22 * Sixth International Conference on Theory and Applications of Satisfiability
23 * Testing, LNCS 2919, pp 502-518, 2003.
24 *
25 * See www.minisat.se for the original solver in C++.
26 *
27 *******************************************************************************/
28 package org.sat4j.minisat.restarts;
29
30 import org.sat4j.minisat.core.RestartStrategy;
31 import org.sat4j.minisat.core.SearchParams;
32
33 /**
34 * Luby series
35 */
36 public class LubyRestarts implements RestartStrategy {
37
38 /**
39 *
40 */
41 private static final long serialVersionUID = 1L;
42
43 private static int[] cachedValues = new int[] { 0, 1, 1, 2 };
44
45 public static final int luby(int i) {
46 if (i >= Integer.MAX_VALUE / 2) {
47 throw new IllegalArgumentException("i is too big");
48 }
49 if (i >= cachedValues.length) {
50 int oldsize = cachedValues.length;
51 int newsize = i << 1;
52 int[] newContent = new int[newsize + 1];
53 System.arraycopy(cachedValues, 0, newContent, 0, oldsize);
54 int nextPowerOfTwo = 1;
55 while (nextPowerOfTwo <= oldsize)
56 nextPowerOfTwo <<= 1;
57
58 int lastPowerOfTwo = nextPowerOfTwo >> 1;
59 for (int j = oldsize; j <= newsize; j++) {
60 if (j + 1 == nextPowerOfTwo) {
61 newContent[j] = lastPowerOfTwo;
62 lastPowerOfTwo = nextPowerOfTwo;
63 nextPowerOfTwo <<= 1;
64 } else {
65 newContent[j] = newContent[j - lastPowerOfTwo + 1];
66 }
67 }
68 cachedValues = newContent;
69
70 }
71 return cachedValues[i];
72 }
73
74 static {
75 // precompute 64 first values
76 luby(32);
77 }
78
79 private int factor;
80
81 private int count;
82
83 public LubyRestarts() {
84 this(32); // uses TiniSAT default
85 }
86
87 /**
88 * @param factor
89 * the factor used for the Luby series.
90 * @since 2.1
91 */
92 public LubyRestarts(int factor) {
93 setFactor(factor);
94 }
95
96 public void setFactor(int factor) {
97 this.factor = factor;
98 }
99
100 public int getFactor() {
101 return factor;
102 }
103
104 public void init(SearchParams params) {
105 count = 1;
106 }
107
108 public long nextRestartNumberOfConflict() {
109 return luby(count) * factor;
110 }
111
112 public void onRestart() {
113 count++;
114 }
115
116 @Override
117 public String toString() {
118 return "luby style (SATZ_rand, TiniSAT) restarts strategy with factor "
119 + factor;
120 }
121
122 }