OCaml arithmetic with no overflow

SafeMath.ml

(* From http://caml.inria.fr/pub/ml-archives/caml-list/2004/06/8730fc362310ad9db0c2239b5b815a22.en.html *)

exception Overflow

let ( + ) a b =
  let c = a + b in
  if (a lxor b) lor (a lxor (lnot c)) < 0 then c else raise Overflow

let ( - ) a b =
  let c = a - b in
  if (a lxor (lnot b)) lor (b lxor c) < 0 then c else raise Overflow

let ( * ) a b =
  let c = a * b in
  if Int64.of_int c = Int64.mul (Int64.of_int a) (Int64.of_int b)
  then c else raise Overflow

let ( / ) a b =
  if a = min_int && b = -1 then raise Overflow else a / b