Definition shr (v w: aval) :=
match w with
| I amount =>
if Int.ltu amount Int.iwordsize then
match v with
| I i => I (Int.shr i amount)
| Uns p n => sgn p (n + 1 - Int.unsigned amount)
| Sgn p n => sgn p (n - Int.unsigned amount)
| _ => sgn (provenance v) (Int.zwordsize - Int.unsigned amount)
end
else ntop1 v
| _ => ntop1 v
end.

Lemma shr_sound:
forall v w x y, vmatch v x -> vmatch w y -> vmatch (Val.shr v w) (shr x y).