(** ** Bit-level reasoning over type [int] *)
Definition testbit (x: int) (i: Z) : bool := Z.testbit (unsigned x) i.

(* Specifications: *)
Lemma testbit_repr:
forall x i,
0 <= i < zwordsize ->
testbit (repr x) i = Z.testbit x i.
Lemma same_bits_eq:
forall x y,
(forall i, 0 <= i < zwordsize -> testbit x i = testbit y i) ->
x = y.
Lemma bits_above:
forall x i, i >= zwordsize -> testbit x i = false.
Lemma bits_zero:
forall i, testbit zero i = false.