(* OK with FLX, FLT and FTZ *)
intros prec Hp x.
case (Req_dec x 0); intros Hxz.
rewrite Hxz, Rabs_R0.
apply bpow_gt_0.
unfold canonic_exp.
destruct (ln_beta beta x) as (ex,Ex) ; simpl.
specialize (Ex Hxz).
apply Rlt_le_trans with (1 := proj2 Ex).
apply bpow_le.
specialize (Hp ex).
omega.
Qed.

Theorem generic_format_bpow_inv :
forall e,
generic_format (bpow e) ->
(fexp e <= e)%Z.