/**********************************************************************
 * Compute the GCD of two integers in base 10 given on the command line.
 * 
 * Usage:
 *  gcd_euclidean <first number> <second number>
 *
 * You may compile the source using GCC 4.x as follows:
 * gcc -std=c99 -pedantic -Wall -Wextra gcd_euclidean.c -o gcd_euclidean
 **********************************************************************/

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


#define NUM_ARGS_NEEDED 3


/**********************************************************************
 * Get the GCD of two numbers using the Euclidean Algorithm.
 *
 * Parameters:
 *  num1 -- the first number
 *  num2 -- the second number
 *
 * Returns:
 *  The GCD of the two numbers, or 0 on error.
 **********************************************************************/
long long get_gcd_euclidean(long long num1, long long num2)
{
  // Temporary variable for swapping the numbers if we need to
  long long temp;
  // The remainder of the two numbers
  long long remainder;

  num1 = llabs(num1);
  num2 = llabs(num2);

  // For the purpose of this algorithm, we need to assume that the
  // first number is the larger of the two
  if (num1 < num2)
  {
    temp = num1;
    num1 = num2;
    num2 = temp;
  }
 
  if (num1 + num2 == 0)
  {
    (void) fprintf(stderr,
                   "%s(%d): Cannot compute the GCD of two zeros.\n",
                   __FILE__, __LINE__);
  }
  if (num1 * num2 == 0)
  {
    // One of the numbers was zero. We are done.
    return num1 + num2;
  }
    
  (void) printf("%lld = (%lld) * (%lld) + %lld\n",
                num1, num1 / num2, num2, num1 % num2);
  // Recursively take the GCD of the smaller number and the
  // remainder of the larger number divided by the smaller number.
  return get_gcd_euclidean(num2, num1 % num2);
}


/**********************************************************************
 * Standard entry point.
 **********************************************************************/
int main(int argc, char* argv[])
{
  // The first number parsed from the command line
  long long num1;
  // The second number parsed from the command line
  long long num2;
  // The GCD of the two numbers
  long long gcd;

  if (argc != NUM_ARGS_NEEDED)
  {
    (void) fprintf(stderr,
                   "%s(%d): Incorrect number of arguments.\n",
                   __FILE__, __LINE__);
    exit(EXIT_FAILURE);
  }

  errno = 0;
  num1 = strtoll(argv[1], NULL, 10);
  if (errno != 0)
  {
    perror("The first integer passed in failed to parse");
    exit(EXIT_FAILURE);
  }

  num2 = strtoll(argv[2], NULL, 10);
  if (errno != 0)
  {
    perror("The second integer passed in failed to parse");
    exit(EXIT_FAILURE);
  }

  gcd = get_gcd_euclidean(num1, num2);
  if (gcd != 0)
  {
    (void) printf("gcd(%lld, %lld) = %lld\n", num1, num2, gcd);
    (void) printf("lcm(%lld, %lld) = %lld\n", num1, num2,
                  (num1 / gcd) * num2);
  }
  else
  {
    (void) printf("Failed to compute gcd(%lld, %lld)\n", num1, num2);
    exit(EXIT_FAILURE);
  }

  exit(EXIT_SUCCESS);
  return 0;
}