Definition shru (v w: aval) :=
  match w with
  | I amount =>
      if Int.ltu amount Int.iwordsize then
        match v with
        | I i => I (Int.shru i amount)
        | Uns p n => uns p (n - Int.unsigned amount)
        | _ => uns (provenance v) (Int.zwordsize - Int.unsigned amount)
        end
      else ntop1 v
  | _ => ntop1 v
  end.

Lemma shru_sound: forall v w x y, vmatch v x -> vmatch w y -> vmatch (Val.shru v w) (shru x y).