/*
 * Function: GCD
 * Usage: gcd = GCD(x, y);
 * -----------------------
 * Returns the greatest common divisor of x and y,
 * calculated by Euclid's algorithm, which is discussed
 * as Proposition 7 in Book II of Euclid's Elements.
 */

int GCD(int x, int y)
{
    int r;

    while (TRUE) {
        r = x % y;
        if (r == 0) break;
        x = y;
        y = r;
    }
    return (y);
}