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------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME COMPONENTS --
-- --
-- S Y S T E M . A T O M I C _ C O U N T E R S --
-- --
-- B o d y --
-- --
-- Copyright (C) 2011-2013, Free Software Foundation, Inc. --
-- --
-- GNAT is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
-- GNAT was originally developed by the GNAT team at New York University. --
-- Extensive contributions were provided by Ada Core Technologies Inc. --
-- --
------------------------------------------------------------------------------
-- This package implements Atomic_Counter operatiobns for platforms where
-- GCC supports __sync_add_and_fetch_4 and __sync_sub_and_fetch_4 builtins.
package body System.Atomic_Counters is
procedure Sync_Add_And_Fetch
(Ptr : access Unsigned_32;
Value : Unsigned_32);
pragma Import (Intrinsic, Sync_Add_And_Fetch, "__sync_add_and_fetch_4");
function Sync_Sub_And_Fetch
(Ptr : access Unsigned_32;
Value : Unsigned_32) return Unsigned_32;
pragma Import (Intrinsic, Sync_Sub_And_Fetch, "__sync_sub_and_fetch_4");
---------------
-- Decrement --
---------------
function Decrement (Item : in out Atomic_Counter) return Boolean is
begin
-- Note: the use of Unrestricted_Access here is required because we
-- are obtaining an access-to-volatile pointer to a non-volatile object.
-- This is not allowed for [Unchecked_]Access, but is safe in this case
-- because we know that no aliases are being created.
return Sync_Sub_And_Fetch (Item.Value'Unrestricted_Access, 1) = 0;
end Decrement;
---------------
-- Increment --
---------------
procedure Increment (Item : in out Atomic_Counter) is
begin
-- Note: the use of Unrestricted_Access here is required because we are
-- obtaining an access-to-volatile pointer to a non-volatile object.
-- This is not allowed for [Unchecked_]Access, but is safe in this case
-- because we know that no aliases are being created.
Sync_Add_And_Fetch (Item.Value'Unrestricted_Access, 1);
end Increment;
----------------
-- Initialize --
----------------
procedure Initialize (Item : out Atomic_Counter) is
begin
Item.Value := 1;
end Initialize;
------------
-- Is_One --
------------
function Is_One (Item : Atomic_Counter) return Boolean is
begin
return Item.Value = 1;
end Is_One;
end System.Atomic_Counters;
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