rewrite Fdigit_abs; auto.
rewrite maxDiv_abs; auto.
Qed.
Definition MSB (x : float) := Zpred (Z_of_nat (Fdigit radix x) + Fexp x).

Theorem MSB_shift :
forall (x : float) (n : nat), ~ is_Fzero x -> MSB x = MSB (Fshift radix n x).