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// Low-level functions for atomic operations: x86, x >= 3 version  -*- C++ -*-

// Copyright (C) 2003, 2004 Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library is free

// software; you can redistribute it and/or modify it under the

// terms of the GNU General Public License as published by the

// Free Software Foundation; either version 2, 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

// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along

// with this library; see the file COPYING.  If not, write to the Free

// Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,

// USA.

// As a special exception, you may use this file as part of a free software

// library without restriction.  Specifically, if other files instantiate

// templates or use macros or inline functions from this file, or you compile

// this file and link it with other files to produce an executable, this

// file does not by itself cause the resulting executable to be covered by

// the GNU General Public License.  This exception does not however

// invalidate any other reasons why the executable file might be covered by

// the GNU General Public License.

#include <bits/atomicity.h>

namespace __gnu_cxx

{

  template<int __inst>

    struct _Atomicity_lock

    {

      static volatile _Atomic_word _S_atomicity_lock;

    };

  template<int __inst>

  volatile _Atomic_word _Atomicity_lock<__inst>::_S_atomicity_lock = 0;

  template volatile _Atomic_word _Atomicity_lock<0>::_S_atomicity_lock;

  _Atomic_word

  __attribute__ ((__unused__))

  __exchange_and_add(volatile _Atomic_word* __mem, int __val)

  {

    register _Atomic_word __result, __tmp = 1;

    // Obtain the atomic exchange/add spin lock.

    do

      {

        __asm__ __volatile__ ("xchg{l} {%0,%1|%1,%0}"

                              : "=m" (_Atomicity_lock<0>::_S_atomicity_lock),

                              "+r" (__tmp)

                              : "m" (_Atomicity_lock<0>::_S_atomicity_lock));

      }

    while (__tmp);

    __result = *__mem;

    *__mem += __val;

    // Release spin lock.

    _Atomicity_lock<0>::_S_atomicity_lock = 0;

    return __result;

  }

  void

  __attribute__ ((__unused__))

  __atomic_add(volatile _Atomic_word* __mem, int __val)

  { __exchange_and_add(__mem, __val); }

} // namespace __gnu_cxx