Fixpoint iterShr8 u n :=
  match n with O => u
   | S n' => Int.shru (iterShr8 u n') (Int.repr 8)
  end.

Lemma Znth_mapVint: forall {d: Inhabitant _} l i, 0<=i< Zlength l -> exists x, Znth i (map Vint l) = Vint x.