Module NZLog2UpProp
(Import A : NZDecOrdAxiomsSig')
(Import B : NZPow' A)
(Import C : NZLog2 A B)
(Import D : NZMulOrderProp A)
(Import E : NZPowProp A B D)
(Import F : NZLog2Prop A B C D E).
(** * [log2_up] : a binary logarithm that rounds up instead of down *)
(** For once, we define instead of axiomatizing, thanks to log2 *)
Definition log2_up a :=
match compare 1 a with
| Lt => S (log2 (P a))
| _ => 0
end.
Instance log2_up_wd : Proper (eq==>eq) log2_up.
(** [log2_up] is always non-negative *)
(** The spec of [log2_up] indeed determines it *)

Lemma log2_up_unique : forall a b, 0<b -> 2^(P b)<a<=2^b -> log2_up a == b.