Computes greatest common divisor of two unlimited-precision integers.
DESCRIPTION
The call gcd_num m n for two unlimited-precision (type num) integers m
and n returns the (positive) greatest common divisor of m and n. If
both m and n are zero, it returns zero.
FAILURE CONDITIONS
Fails if either number is not an integer (the type num supports arbitrary
rationals).
EXAMPLE
# gcd_num (Int 35) (Int(-77));;
val it : num = 7
# gcd_num (Int 11) (Int 0);;
val it : num = 11
# gcd_num (Int 22 // Int 7) (Int 2);;
Exception: Failure "big_int_of_ratio".