/*
 * 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.
 *
 * This file is a derivative of code released by the University of
 * California under the terms listed below.
 *
 * Refinement Analysis Tools is Copyright (c) 2007 The Regents of the
 * University of California (Regents). Provided that this notice and
 * the following two paragraphs are included in any distribution of
 * Refinement Analysis Tools or its derivative work, Regents agrees
 * not to assert any of Regents' copyright rights in Refinement
 * Analysis Tools against recipient for recipient's reproduction,
 * preparation of derivative works, public display, public
 * performance, distribution or sublicensing of Refinement Analysis
 * Tools and derivative works, in source code and object code form.
 * This agreement not to assert does not confer, by implication,
 * estoppel, or otherwise any license or rights in any intellectual
 * property of Regents, including, but not limited to, any patents
 * of Regents or Regents' employees.
 *
 * IN NO EVENT SHALL REGENTS BE LIABLE TO ANY PARTY FOR DIRECT,
 * INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES,
 * INCLUDING LOST PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE
 * AND ITS DOCUMENTATION, EVEN IF REGENTS HAS BEEN ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 *
 * REGENTS SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE AND FURTHER DISCLAIMS ANY STATUTORY
 * WARRANTY OF NON-INFRINGEMENT. THE SOFTWARE AND ACCOMPANYING
 * DOCUMENTATION, IF ANY, PROVIDED HEREUNDER IS PROVIDED "AS
 * IS". REGENTS HAS NO OBLIGATION TO PROVIDE MAINTENANCE, SUPPORT,
 * UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 */
package com.ibm.wala.util.math;

import java.math.BigInteger;

/** Factorial utilities */
public class Factorial {

  /** Factorial */
  public static long fact(long n) {
    long result = 1;
    for (long i = 1; i <= n; i++) result *= i;
    return result;
  }

  /** Factorial */
  public static BigInteger fact(BigInteger n) {
    if (n == null) {
      throw new IllegalArgumentException("n is null");
    }
    BigInteger result = BigInteger.ONE;
    for (BigInteger i = BigInteger.ONE; i.compareTo(n) <= 0; i = i.add(BigInteger.ONE)) {
      result = result.multiply(i);
    }
    return result;
  }

  /**
   * Factorial on doubles; avoids overflow problems present when using integers.
   *
   * @param n arg on which to compute factorial
   * @return (<code>double</code> approximation to) factorial of largest positive integer &lt;= (n_
   *     + epsilon)
   */
  public static double fact(double n) {
    n += 1e-6;
    double result = 1.0;
    for (double i = 1; i <= n; i += 1.0) result *= i;
    return result;
  }

  /** Factorial */
  public static int fact(int n) {
    int result = 1;
    for (int i = 1; i <= n; i++) result *= i;
    return result;
  }
}
