gcd

fntypeof(Unqual!(T).init % Unqual!(U).init) gcd(T, U)(T a, U b) if (isIntegral!T && isIntegral!U)

Computes the greatest common divisor of a and b by using an efficient algorithm such as Euclid's or Stein's algorithm.

`a`	Integer value of any numerical type that supports the modulo operator `%`. If bit-shifting `<<` and `>>` are also supported, Stein's algorithm will be used; otherwise, Euclid's algorithm is used as _a fallback.
`b`	Integer value of any equivalent numerical type.

The greatest common divisor of the given arguments.

auto gcd(T)(T a,  T b) if (!isIntegral!T &&
         is(typeof(T.init %  T.init))  &&
         is(typeof(T.init ==  0 ||  T.init >  0)))

ditto