> So it is not easy, perhaps even impossible if the processor doesn't set a
> flag .

It is possible, but slow and not pretty!  For example, here is Caml
code that performs integer addition and detects overflows:

exception Integer_overflow

let no_overflow_add a b = 
  if (a lxor b) lor (a lxor (lnot (a+b))) < 0  (* no kidding! *)
  then a + b
  else raise Integer_overflow

Multiplication is left as an exercise for the readers :-)

My advice would be to use bignums; they are a bit slower, but at least
you get the exact result in all cases.

- Xavier Leroy
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