Definition sintv (v: aval) : Z * Z :=
  match v with
  | I n => (Int.signed n, Int.signed n)
  | Uns _ n =>
      if zlt n Int.zwordsize then (0, two_p n - 1) else (Int.min_signed, Int.max_signed)
  | Sgn _ n =>
      if zlt n Int.zwordsize
      then (let x := two_p (n-1) in (-x, x-1))
      else (Int.min_signed, Int.max_signed)
  | _ => (Int.min_signed, Int.max_signed)
  end.

Lemma cmp_intv_sound: forall c n1 v1 n2, vmatch (Vint n1) v1 -> cmatch (Val.cmp_bool c (Vint n1) (Vint n2)) (cmp_intv c (sintv v1) (Int.signed n2)).