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.

Lemma log2_up_spec : forall a, 1<a ->
2^(P (log2_up a)) < a <= 2^(log2_up a).