(************************************************************************)
(*         *      The Rocq Prover / The Rocq Development Team           *)
(*  v      *         Copyright INRIA, CNRS and contributors             *)
(* <O___,, * (see version control and CREDITS file for authors & dates) *)
(*   \VV/  **************************************************************)
(*    //   *    This file is distributed under the terms of the         *)
(*         *     GNU Lesser General Public License Version 2.1          *)
(*         *     (see LICENSE file for the text of the license)         *)
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(** Axiomatization of some bitwise operations *)
Module Type Bits (Import A : Typ).
Parameter Inline testbit : t -> t -> bool.
Parameters Inline shiftl shiftr land lor ldiff lxor : t -> t -> t.
Parameter Inline div2 : t -> t.
End Bits.
Module Type BitsNotation (Import A : Typ)(Import B : Bits A).
Notation "a .[ n ]" := (testbit a n) (at level 5, format "a .[ n ]").
Infix ">>" := shiftr (at level 30, no associativity).
Infix "<<" := shiftl (at level 30, no associativity).
End BitsNotation.
Module Type Bits' (A:Typ) := Bits A <+ BitsNotation A.
Module Type NZBitsSpec
(Import A : NZOrdAxiomsSig')(Import B : Bits' A).
#[global]
Declare Instance testbit_wd : Proper (eq==>eq==>Logic.eq) testbit.

(* Specifications: *)
Axiom testbit_odd_0 : forall a, (2*a+1).[0] = true.
Axiom testbit_even_0 : forall a, (2*a).[0] = false.
Axiom testbit_odd_succ : forall a n, 0<=n -> (2*a+1).[S n] = a.[n].
Axiom testbit_even_succ : forall a n, 0<=n -> (2*a).[S n] = a.[n].
Axiom testbit_neg_r : forall a n, n<0 -> a.[n] = false.
Axiom shiftr_spec : forall a n m, 0<=m -> (a >> n).[m] = a.[m+n].
Axiom shiftl_spec_high : forall a n m, 0<=m -> n<=m -> (a << n).[m] = a.[m-n].
Axiom shiftl_spec_low : forall a n m, m<n -> (a << n).[m] = false.
Axiom land_spec : forall a b n, (land a b).[n] = a.[n] && b.[n].
Axiom lor_spec : forall a b n, (lor a b).[n] = a.[n] || b.[n].
Axiom ldiff_spec : forall a b n, (ldiff a b).[n] = a.[n] && negb b.[n].
Axiom lxor_spec : forall a b n, (lxor a b).[n] = xorb a.[n] b.[n].
Axiom div2_spec : forall a, div2 a == a >> 1.
End NZBitsSpec.