(** This file is part of the Flocq formalization of floating-point arithmetic in Coq: http://flocq.gforge.inria.fr/  Copyright (C) 2010-2013 Sylvie Boldo #<br /># Copyright (C) 2010-2013 Guillaume Melquiond  This library is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.  This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the COPYING file for more details. *)
(** * Roundings: properties and/or functions *)
Section RND_prop.
Open Scope R_scope.

(* Specifications: *)
Theorem round_val_of_pred :
forall rnd : R -> R -> Prop,
round_pred rnd ->
forall x, { f : R | rnd x f }.
Theorem round_fun_of_pred :
forall rnd : R -> R -> Prop,
round_pred rnd ->
{ f : R -> R | forall x, rnd x (f x) }.
Theorem round_unicity :
forall rnd : R -> R -> Prop,
round_pred_monotone rnd ->
forall x f1 f2,
rnd x f1 ->
rnd x f2 ->
f1 = f2.
Theorem Rnd_DN_pt_monotone :
forall F : R -> Prop,
round_pred_monotone (Rnd_DN_pt F).
Theorem Rnd_DN_pt_unicity :
forall F : R -> Prop,
forall x f1 f2 : R,
Rnd_DN_pt F x f1 -> Rnd_DN_pt F x f2 ->
f1 = f2.
Theorem Rnd_DN_unicity :
forall F : R -> Prop,
forall rnd1 rnd2 : R -> R,
Rnd_DN F rnd1 -> Rnd_DN F rnd2 ->
forall x, rnd1 x = rnd2 x.
Theorem Rnd_UP_pt_monotone :
forall F : R -> Prop,
round_pred_monotone (Rnd_UP_pt F).
Theorem Rnd_UP_pt_unicity :
forall F : R -> Prop,
forall x f1 f2 : R,
Rnd_UP_pt F x f1 -> Rnd_UP_pt F x f2 ->
f1 = f2.
Theorem Rnd_UP_unicity :
forall F : R -> Prop,
forall rnd1 rnd2 : R -> R,
Rnd_UP F rnd1 -> Rnd_UP F rnd2 ->
forall x, rnd1 x = rnd2 x.
Theorem Rnd_DN_UP_pt_sym :
forall F : R -> Prop,
( forall x, F x -> F (- x) ) ->
forall x f : R,
Rnd_DN_pt F x f -> Rnd_UP_pt F (-x) (-f).
Theorem Rnd_UP_DN_pt_sym :
forall F : R -> Prop,
( forall x, F x -> F (- x) ) ->
forall x f : R,
Rnd_UP_pt F x f -> Rnd_DN_pt F (-x) (-f).
Theorem Rnd_DN_UP_sym :
forall F : R -> Prop,
( forall x, F x -> F (- x) ) ->
forall rnd1 rnd2 : R -> R,
Rnd_DN F rnd1 -> Rnd_UP F rnd2 ->
forall x, rnd1 (- x) = - rnd2 x.
Theorem Rnd_DN_UP_pt_split :
forall F : R -> Prop,
forall x d u,
Rnd_DN_pt F x d ->
Rnd_UP_pt F x u ->
forall f, F f ->
(f <= d) \/ (u <= f).
Theorem Rnd_DN_pt_refl :
forall F : R -> Prop,
forall x : R, F x ->
Rnd_DN_pt F x x.
Theorem Rnd_DN_pt_idempotent :
forall F : R -> Prop,
forall x f : R,
Rnd_DN_pt F x f -> F x ->
f = x.
Theorem Rnd_UP_pt_refl :
forall F : R -> Prop,
forall x : R, F x ->
Rnd_UP_pt F x x.
Theorem Rnd_UP_pt_idempotent :
forall F : R -> Prop,
forall x f : R,
Rnd_UP_pt F x f -> F x ->
f = x.
Theorem Only_DN_or_UP :
forall F : R -> Prop,
forall x fd fu f : R,
Rnd_DN_pt F x fd -> Rnd_UP_pt F x fu ->
F f -> (fd <= f <= fu)%R ->
f = fd \/ f = fu.
Theorem Rnd_ZR_abs :
forall (F : R -> Prop) (rnd: R-> R),
Rnd_ZR F rnd ->
forall x : R,  (Rabs (rnd x) <= Rabs x)%R.
Theorem Rnd_ZR_pt_monotone :
forall F : R -> Prop, F 0 ->
round_pred_monotone (Rnd_ZR_pt F).
Theorem Rnd_N_pt_DN_or_UP :
forall F : R -> Prop,
forall x f : R,
Rnd_N_pt F x f ->
Rnd_DN_pt F x f \/ Rnd_UP_pt F x f.
Theorem Rnd_N_pt_DN_or_UP_eq :
forall F : R -> Prop,
forall x fd fu f : R,
Rnd_DN_pt F x fd -> Rnd_UP_pt F x fu ->
Rnd_N_pt F x f ->
f = fd \/ f = fu.
Theorem Rnd_N_pt_sym :
forall F : R -> Prop,
( forall x, F x -> F (- x) ) ->
forall x f : R,
Rnd_N_pt F (-x) (-f) -> Rnd_N_pt F x f.
Theorem Rnd_N_pt_monotone :
forall F : R -> Prop,
forall x y f g : R,
Rnd_N_pt F x f -> Rnd_N_pt F y g ->
x < y -> f <= g.
Theorem Rnd_N_pt_unicity :
forall F : R -> Prop,
forall x d u f1 f2 : R,
Rnd_DN_pt F x d ->
Rnd_UP_pt F x u ->
x - d <> u - x ->
Rnd_N_pt F x f1 ->
Rnd_N_pt F x f2 ->
f1 = f2.
Theorem Rnd_N_pt_refl :
forall F : R -> Prop,
forall x : R, F x ->
Rnd_N_pt F x x.
Theorem Rnd_N_pt_idempotent :
forall F : R -> Prop,
forall x f : R,
Rnd_N_pt F x f -> F x ->
f = x.
Theorem Rnd_N_pt_0 :
forall F : R -> Prop,
F 0 ->
Rnd_N_pt F 0 0.
Theorem Rnd_N_pt_pos :
forall F : R -> Prop, F 0 ->
forall x f, 0 <= x ->
Rnd_N_pt F x f ->
0 <= f.
Theorem Rnd_N_pt_neg :
forall F : R -> Prop, F 0 ->
forall x f, x <= 0 ->
Rnd_N_pt F x f ->
f <= 0.
Theorem Rnd_N_pt_abs :
forall F : R -> Prop,
F 0 ->
( forall x, F x -> F (- x) ) ->
forall x f : R,
Rnd_N_pt F x f -> Rnd_N_pt F (Rabs x) (Rabs f).
Theorem Rnd_DN_UP_pt_N :
forall F : R -> Prop,
forall x d u f : R,
F f ->
Rnd_DN_pt F x d ->
Rnd_UP_pt F x u ->
(Rabs (f - x) <= x - d)%R ->
(Rabs (f - x) <= u - x)%R ->
Rnd_N_pt F x f.
Theorem Rnd_DN_pt_N :
forall F : R -> Prop,
forall x d u : R,
Rnd_DN_pt F x d ->
Rnd_UP_pt F x u ->
(x - d <= u - x)%R ->
Rnd_N_pt F x d.
Theorem Rnd_UP_pt_N :
forall F : R -> Prop,
forall x d u : R,
Rnd_DN_pt F x d ->
Rnd_UP_pt F x u ->
(u - x <= x - d)%R ->
Rnd_N_pt F x u.