1 /*******************************************************************************
2 * SAT4J: a SATisfiability library for Java Copyright (C) 2004, 2012 Artois University and CNRS
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 * Contributors:
28 * CRIL - initial API and implementation
29 *******************************************************************************/
30 package org.sat4j.minisat.orders;
31
32 /**
33 * @author leberre TODO To change the template for this generated type comment
34 * go to Window - Preferences - Java - Code Style - Code Templates
35 */
36 public final class PureOrder extends VarOrderHeap {
37
38 /**
39 * Comment for <code>serialVersionUID</code>
40 */
41 private static final long serialVersionUID = 1L;
42
43 private int period;
44
45 private int cpt;
46
47 public PureOrder() {
48 this(20);
49 }
50
51 public PureOrder(int p) {
52 setPeriod(p);
53 }
54
55 public final void setPeriod(int p) {
56 this.period = p;
57 this.cpt = this.period;
58 }
59
60 public int getPeriod() {
61 return this.period;
62 }
63
64 /*
65 * (non-Javadoc)
66 *
67 * @see org.sat4j.minisat.core.VarOrder#select()
68 */
69 @Override
70 public int select() {
71 // wait period branching
72 if (this.cpt < this.period) {
73 this.cpt++;
74 } else {
75 // try to find a pure literal
76 this.cpt = 0;
77 int nblits = 2 * this.lits.nVars();
78 for (int i = 2; i <= nblits; i++) {
79 if (this.lits.isUnassigned(i)
80 && this.lits.watches(i).size() > 0
81 && this.lits.watches(i ^ 1).size() == 0) {
82 return i;
83 }
84 }
85 }
86 // not found: using normal order
87 return super.select();
88 }
89
90 @Override
91 public String toString() {
92 return "tries to first branch on a single phase watched unassigned variable (pure literal if using a CB data structure) else VSIDS from MiniSAT"; //$NON-NLS-1$
93 }
94 }