/* ***** BEGIN LICENSE BLOCK *****
 * Version: GPL 2.0
 *
 * gcd.c : an implementation of the Euclidean Algorithm
 * Copyright (C) 2007  Adam Dane
 *
 * First Edit: 2007.10.11
 * Last Edit: 2007.10.12
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 *
 * ***** END LICENSE BLOCK ***** */

#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
#include <errno.h>

int
main(int argc, char **argv)
{
  int a,b,r; //declare variables

  if (argc < 3)
  {
    printf("usage: gcd <value> <value> where neither == 0\n");
    exit(-1);
  }

  b = strtol(argv[1], NULL, 10); // get values from command line 
  if (errno != 0 && (b == LONG_MIN || b == LONG_MAX)) // ensure valid input
  {
    perror("Bad argument");
    exit(-1);
  }
  
  r = strtol(argv[2], NULL, 10);
  if (errno != 0 && (r == LONG_MIN || r == LONG_MAX))
  {
    perror("Bad argument");
    exit(-1);
  }

  if (b < r) // order them properly
  {
    a = r;
    r = b;
    b = a;
  }

  while (r != 0) // keep going until GCD found (worst case it's 1)
  {
    a = b; // shuffle values to correct spots
    b = r;

    if ((r = a % b) == 0) // compute the remainder, if it's 0 then GCD found 
    {
      printf("The GCD is: %d\n", b);
      exit(0);
    }
  }
  printf("usage: gcd <value> <value> where neither == 0\n");
  exit(-1);
}