(* works, but very slow! Lemma exp_table_correct : forall a : nat, (a < 256)%nat -> nth a ff_exp_table Int.zero = exp3 a. *)

Lemma ff_exp_step: forall a e,
0 <= Int.unsigned a < 256 ->
0 <= e < Int.max_signed ->
ff_exp a (Int.repr (1 + e)) = ff_mult a (ff_exp a (Int.repr e)).