Definition double d :=
match d with
| Pos u => Pos (Unsigned.double u)
| Neg u => Neg (Unsigned.double u)
end.

(* Specifications: *)
Lemma double_norm d : double (norm d) = norm (double d).
Lemma of_hex_int_double d :
Z.of_hex_int (double d) = Z.double (Z.of_hex_int d).
Lemma double_to_hex_int n :
double (Z.to_hex_int n) = Z.to_hex_int (Z.double n).