/* gcd.c - simple example of calculating GCD (greatest common divisor 
 * Jon Mayo - PUBLIC DOMAIN - July 24, 2007 */
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv) {
    long a, b;
    
    if(argc!=3) {
        fprintf(stderr, "Usage: %s <integer> <integer>\n", argv[0]);
        return EXIT_FAILURE;
    }
    a=strtol(argv[1], 0, 0);
    b=strtol(argv[2], 0, 0);

    if(a==0 && b==0) {
        printf("gdc=N/A\n");
        return EXIT_FAILURE;
    }

    /* subtract smallest from largest in a loop. swap to keep b the smallest.
     * result of GDC will be in a (the largest) */
    while(b!=0) {
        /* printf("a=%ld\n", a); */
        if(a>=b) {
            a-=b;
        } else {
            /* swap(a,b) */
            a^=b;
            b^=a;
            a^=b;
        }
    }
    printf("gdc=%ld\n", a);
    return 0;
}