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------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME COMPONENTS --
-- --
-- System.Atomic_Operations.Modular_Arithmetic --
-- --
-- B o d y --
-- --
-- Copyright (C) 2019-2021, 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. --
-- --
------------------------------------------------------------------------------
with System.Atomic_Primitives; use System.Atomic_Primitives;
with System.Atomic_Operations.Exchange;
with Interfaces.C; use Interfaces;
package body System.Atomic_Operations.Modular_Arithmetic is
package Exchange is new System.Atomic_Operations.Exchange (Atomic_Type);
----------------
-- Atomic_Add --
----------------
procedure Atomic_Add
(Item : aliased in out Atomic_Type;
Value : Atomic_Type)
is
Ignore : constant Atomic_Type := Atomic_Fetch_And_Add (Item, Value);
begin
null;
end Atomic_Add;
---------------------
-- Atomic_Subtract --
---------------------
procedure Atomic_Subtract
(Item : aliased in out Atomic_Type;
Value : Atomic_Type)
is
Ignore : constant Atomic_Type := Atomic_Fetch_And_Subtract (Item, Value);
begin
null;
end Atomic_Subtract;
--------------------------
-- Atomic_Fetch_And_Add --
--------------------------
function Atomic_Fetch_And_Add
(Item : aliased in out Atomic_Type;
Value : Atomic_Type) return Atomic_Type
is
pragma Warnings (Off);
function Atomic_Fetch_Add
(Ptr : System.Address; Val : Atomic_Type; Model : Mem_Model := Seq_Cst)
return Atomic_Type;
pragma Import (Intrinsic, Atomic_Fetch_Add, "__atomic_fetch_add");
pragma Warnings (On);
begin
-- Use the direct intrinsics when possible, and fallback to
-- compare-and-exchange otherwise.
if Atomic_Type'Base'Last = Atomic_Type'Last
and then Atomic_Type'First = 0
and then Atomic_Type'Last = 2**Atomic_Type'Object_Size - 1
then
if Atomic_Type'Object_Size in 8 | 16 | 32 | 64 then
return Atomic_Fetch_Add (Item'Address, Value);
else
raise Program_Error;
end if;
else
declare
Old_Value : aliased Atomic_Type := Item;
New_Value : Atomic_Type := Old_Value + Value;
begin
-- Keep iterating until the exchange succeeds
while not Exchange.Atomic_Compare_And_Exchange
(Item, Old_Value, New_Value)
loop
New_Value := Old_Value + Value;
end loop;
return Old_Value;
end;
end if;
end Atomic_Fetch_And_Add;
-------------------------------
-- Atomic_Fetch_And_Subtract --
-------------------------------
function Atomic_Fetch_And_Subtract
(Item : aliased in out Atomic_Type;
Value : Atomic_Type) return Atomic_Type
is
pragma Warnings (Off);
function Atomic_Fetch_Sub
(Ptr : System.Address; Val : Atomic_Type; Model : Mem_Model := Seq_Cst)
return Atomic_Type;
pragma Import (Intrinsic, Atomic_Fetch_Sub, "__atomic_fetch_sub");
pragma Warnings (On);
begin
-- Use the direct intrinsics when possible, and fallback to
-- compare-and-exchange otherwise.
if Atomic_Type'Base'Last = Atomic_Type'Last
and then Atomic_Type'First = 0
and then Atomic_Type'Last = 2**Atomic_Type'Object_Size - 1
then
if Atomic_Type'Object_Size in 8 | 16 | 32 | 64 then
return Atomic_Fetch_Sub (Item'Address, Value);
else
raise Program_Error;
end if;
else
declare
Old_Value : aliased Atomic_Type := Item;
New_Value : Atomic_Type := Old_Value - Value;
begin
-- Keep iterating until the exchange succeeds
while not Exchange.Atomic_Compare_And_Exchange
(Item, Old_Value, New_Value)
loop
New_Value := Old_Value - Value;
end loop;
return Old_Value;
end;
end if;
end Atomic_Fetch_And_Subtract;
------------------
-- Is_Lock_Free --
------------------
function Is_Lock_Free (Item : aliased Atomic_Type) return Boolean is
pragma Unreferenced (Item);
use type Interfaces.C.size_t;
begin
return Atomic_Always_Lock_Free (Atomic_Type'Object_Size / 8);
end Is_Lock_Free;
end System.Atomic_Operations.Modular_Arithmetic;