(* 3^e in GF(2^8) *)
Definition exp3 (e: nat): int := ff_exp (Int.repr 3) (Int.repr (Z.of_nat e)).

Lemma ff_exp_range: forall a b, 0 <= a < 256 -> 0 <= b < 256 -> 0 <= Int.unsigned (ff_exp (Int.repr a) (Int.repr b)) < 256.