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