Definition split_bits x :=
let mm := Zpower 2 mw in
let em := Zpower 2 ew in
(Zle_bool (mm * em) x, Zmod x mm, Zmod (Zdiv x mm) em)%Z.

(* Specifications: *)
Theorem split_join_bits :
forall s m e,
(0 <= m < Zpower 2 mw)%Z ->
(0 <= e < Zpower 2 ew)%Z ->
split_bits (join_bits s m e) = (s, m, e).
Theorem join_split_bits :
forall x,
(0 <= x < Zpower 2 (mw + ew + 1))%Z ->
let '(s, m, e) := split_bits x in
join_bits s m e = x.
Theorem split_bits_inj :
forall x y,
(0 <= x < Zpower 2 (mw + ew + 1))%Z ->
(0 <= y < Zpower 2 (mw + ew + 1))%Z ->
split_bits x = split_bits y ->
x = y.