Greatest Common Divisor (GCD) of positive integer numbers

        
/*
 * $RCSfile: MathUtil.java,v $
 * $Revision: 1.1 $
 * $Date: 2005/02/11 05:02:25 $
 * $State: Exp $
 *
 * Class:                   MathUtil
 *
 * Description:             Utility mathematical methods
 *
 *
 *
 * COPYRIGHT:
 *
 * This software module was originally developed by Raphal Grosbois and
 * Diego Santa Cruz (Swiss Federal Institute of Technology-EPFL); Joel
 * Askelf (Ericsson Radio Systems AB); and Bertrand Berthelot, David
 * Bouchard, Flix Henry, Gerard Mozelle and Patrice Onno (Canon Research
 * Centre France S.A) in the course of development of the JPEG2000
 * standard as specified by ISO/IEC 15444 (JPEG 2000 Standard). This
 * software module is an implementation of a part of the JPEG 2000
 * Standard. Swiss Federal Institute of Technology-EPFL, Ericsson Radio
 * Systems AB and Canon Research Centre France S.A (collectively JJ2000
 * Partners) agree not to assert against ISO/IEC and users of the JPEG
 * 2000 Standard (Users) any of their rights under the copyright, not
 * including other intellectual property rights, for this software module
 * with respect to the usage by ISO/IEC and Users of this software module
 * or modifications thereof for use in hardware or software products
 * claiming conformance to the JPEG 2000 Standard. Those intending to use
 * this software module in hardware or software products are advised that
 * their use may infringe existing patents. The original developers of
 * this software module, JJ2000 Partners and ISO/IEC assume no liability
 * for use of this software module or modifications thereof. No license
 * or right to this software module is granted for non JPEG 2000 Standard
 * conforming products. JJ2000 Partners have full right to use this
 * software module for his/her own purpose, assign or donate this
 * software module to any third party and to inhibit third parties from
 * using this software module for non JPEG 2000 Standard conforming
 * products. This copyright notice must be included in all copies or
 * derivative works of this software module.
 *
 * Copyright (c) 1999/2000 JJ2000 Partners.
 * */



/**
 * This class contains a collection of utility methods fro mathematical
 * operations. All methods are static.
 * */
public class MathUtil {

  /** 
   * Method that calculates the Greatest Common Divisor (GCD) of several
   * positive integer numbers.
   *
   * @param x Array containing the numbers.
   * */
  public static final int gcd(int[] x) {
      if(x.length<2) {
          throw new Error("Do not use this method if there are less than"+
                          " two numbers.");
      }
      int tmp = gcd(x[x.length-1],x[x.length-2]);
      for(int i=x.length-3; i>=0; i--) {
          if(x[i]<0) {
              throw new IllegalArgumentException("Cannot compute the least "+
                                                 "common multiple of "+
                                                 "several numbers where "+
                                                 "one, at least,"+
                                                 "is negative.");
          }
          tmp = gcd(tmp,x[i]);
      }
      return tmp;
  }

  /** 
   * Method that calculates the Greatest Common Divisor (GCD) of two
   * positive integer numbers.
   * */
  public static final int gcd(int x1,int x2) {
      if(x1<0 || x2<0) {
          throw new IllegalArgumentException("Cannot compute the GCD "+
                                             "if one integer is negative.");
      }
      int a,b,g,z;

      if(x1>x2) {
          a = x1;
          b = x2;
      } else {
          a = x2;
          b = x1;
      }

      if(b==0) return 0;

      g = b;
      while (g!=0) {
          z= a%g;
          a = g;
          g = z;
      }
      return a;
  }

}

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Greatest Common Divisor (GCD) of positive integer numbers : Math « Development Class « Java

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