Hint Rewrite bits_zero bits_mone : ints.
Ltac bit_solve :=
intros; apply same_bits_eq; intros; autorewrite with ints; auto with bool.

Lemma bits_signed:
forall x i, 0 <= i ->
Z.testbit (signed x) i = testbit x (if zlt i zwordsize then i else zwordsize - 1).