Definition canonic_exp x :=
  fexp (ln_beta beta x).Definition canonic (f : float beta) :=
  Fexp f = canonic_exp (F2R f).Definition scaled_mantissa x :=
  (x * bpow (- canonic_exp x))%R.Definition generic_format (x : R) :=
  x = F2R (Float beta (Ztrunc (scaled_mantissa x)) (canonic_exp x)).

Theorem mantissa_UP_small_pos : forall x ex, (bpow (ex - 1) <= x < bpow ex)%R -> (ex <= fexp ex)%Z -> Zceil (x * bpow (- fexp ex)) = 1%Z.