/*******************************************************************************
* SAT4J: a SATisfiability library for Java Copyright (C) 2004-2008 Daniel Le Berre
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Alternatively, the contents of this file may be used under the terms of
* either the GNU Lesser General Public License Version 2.1 or later (the
* "LGPL"), in which case the provisions of the LGPL are applicable instead
* of those above. If you wish to allow use of your version of this file only
* under the terms of the LGPL, and not to allow others to use your version of
* this file under the terms of the EPL, indicate your decision by deleting
* the provisions above and replace them with the notice and other provisions
* required by the LGPL. If you do not delete the provisions above, a recipient
* may use your version of this file under the terms of the EPL or the LGPL.
*
* Based on the original MiniSat specification from:
*
* An extensible SAT solver. Niklas Een and Niklas Sorensson. Proceedings of the
* Sixth International Conference on Theory and Applications of Satisfiability
* Testing, LNCS 2919, pp 502-518, 2003.
*
* See www.minisat.se for the original solver in C++.
*
*******************************************************************************/
package org.sat4j.core;
/**
* Utility methods to avoid using bit manipulation inside code. One should use
* Java 1.5 import static feature to use it without class qualification inside
* the code.
*
* In the DIMACS format, the literals are represented by signed integers, 0
* denoting the end of the clause. In the solver, the literals are represented
* by positive integers, in order to use them as index in arrays for instance.
*
* <pre>
* int p : a literal (p>1)
* p ˆ 1 : the negation of the literal
* p >> 1 : the DIMACS number reresenting the variable.
* int v : a DIMACS variable (v>0)
* v << 1 : a positive literal for that variable in the solver.
* v << 1 ˆ 1 : a negative literal for that variable.
* </pre>
*
* @author leberre
*
*/
public final class LiteralsUtils {
private LiteralsUtils() {
// no instance supposed to be created.
}
/**
* Returns the variable associated to the literal
* @param p a literal
* @return the variable associated to that literal.
*/
public static int var(int p) {
assert p > 1;
return p >> 1;
}
/**
* Returns the opposite literal.
*
* @param p a literal
* @return the opposite literal
*/
public static int neg(int p) {
return p ^ 1;
}
/**
* Returns the positive literal associated with a variable.
* @param var a variable
* @return the positive literal associated to this variable.
*/
public static int posLit(int var) {
return var << 1;
}
/**
* Returns the negative literal associated with a variable.
* @param var a variable.
* @return the negative literal associated with var.
*/
public static int negLit(int var) {
return (var << 1)^1;
}
/**
* decode the internal representation of a literal into Dimacs format.
*
* @param p
* the literal in internal representation
* @return the literal in dimacs representation
*/
public static int toDimacs(int p) {
return ((p & 1) == 0 ? 1 : -1) * (p >> 1);
}
}