intros rnd x Hx.
unfold round, scaled_mantissa.
rewrite canonic_exp_FLT_FLX ; trivial.
Qed.

(** Links between FLT and FIX (underflow) *)
Theorem canonic_exp_FLT_FIX :
forall x, x <> 0%R ->
(Rabs x < bpow (emin + prec))%R ->
canonic_exp beta FLT_exp x = canonic_exp beta (FIX_exp emin) x.