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 *
 * 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
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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 (double approximation to) factorial of largest positive integer <= (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;
  }
}