Hint Rewrite bits_shl bits_shru bits_shr: ints.

Lemma bitwise_binop_shr:
forall f f' x y n,
(forall x y i, 0 <= i < zwordsize -> testbit (f x y) i = f' (testbit x i) (testbit y i)) ->
f (shr x n) (shr y n) = shr (f x y) n.