Definition data_block {cs: compspecs} (sh: share) (contents: list byte) :=
  @data_at cs sh (tarray tuchar (Zlength contents)) (map Vubyte contents).

Lemma nth_mapVintZ: forall i (l:list Z) (Hi: 0 <= i < Zlength l), exists n, nth (Z.to_nat i) (map Vint (map Int.repr l)) Vundef = Vint n.