org.jgrapht.util.MathUtil Maven / Gradle / Ivy
/*
* (C) Copyright 2005-2021, by Assaf Lehr and Contributors.
*
* JGraphT : a free Java graph-theory library
*
* See the CONTRIBUTORS.md file distributed with this work for additional
* information regarding copyright ownership.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License 2.0 which is available at
* http://www.eclipse.org/legal/epl-2.0, or the
* GNU Lesser General Public License v2.1 or later
* which is available at
* http://www.gnu.org/licenses/old-licenses/lgpl-2.1-standalone.html.
*
* SPDX-License-Identifier: EPL-2.0 OR LGPL-2.1-or-later
*/
package org.jgrapht.util;
/**
* Math Utilities.
*
* @author Assaf Lehr
*/
public class MathUtil
{
/**
* Calculate the factorial of $n$.
*
* @param n the input number
* @return the factorial
*/
public static long factorial(int n)
{
long multi = 1;
for (int i = 1; i <= n; i++) {
multi = multi * i;
}
return multi;
}
/**
* Calculate the floor of the binary logarithm of $n$.
*
* @param n the input number
* @return the binary logarithm
*/
public static int log2(int n)
{
// returns 0 for n=0
int log = 0;
if ((n & 0xffff0000) != 0) {
n >>>= 16;
log = 16;
}
if (n >= 256) {
n >>>= 8;
log += 8;
}
if (n >= 16) {
n >>>= 4;
log += 4;
}
if (n >= 4) {
n >>>= 2;
log += 2;
}
return log + (n >>> 1);
}
}