(* a list initialized with 0 except its last i elements *)
Definition list_zero_except (i : Z) (size : Z) : list val :=
  (list_repeat (Z.to_nat (size-i)) (Vint Int.zero)) ++ (list_repeat (Z.to_nat i) Vundef).

Lemma Z_repr_0_unsigned: forall n, 0 <= n <= Int.max_unsigned -> Int.repr n = Int.zero -> n = 0.