atomic_base.h

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// -*- C++ -*- header.

// Copyright (C) 2008, 2009, 2010, 2011, 2012 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 3, 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.

// 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/>.

/** @file bits/atomic_base.h
 *  This is an internal header file, included by other library headers.
 *  Do not attempt to use it directly. @headername{atomic}
 */

#ifndef _GLIBCXX_ATOMIC_BASE_H
#define _GLIBCXX_ATOMIC_BASE_H 1

#pragma GCC system_header

#include <bits/c++config.h>
#include <stdbool.h>
#include <stdint.h>
#include <bits/atomic_lockfree_defines.h>

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  /**
   * @defgroup atomics Atomics
   *
   * Components for performing atomic operations.
   * @{
   */

  /// Enumeration for memory_order
  typedef enum memory_order
    {
      memory_order_relaxed,
      memory_order_consume,
      memory_order_acquire,
      memory_order_release,
      memory_order_acq_rel,
      memory_order_seq_cst
    } memory_order;

  // Drop release ordering as per [atomics.types.operations.req]/21
  constexpr memory_order
  __cmpexch_failure_order(memory_order __m) noexcept
  {
    return __m == memory_order_acq_rel ? memory_order_acquire
      : __m == memory_order_release ? memory_order_relaxed : __m;
  }

  inline void
  atomic_thread_fence(memory_order __m) noexcept
  { __atomic_thread_fence(__m); }

  inline void
  atomic_signal_fence(memory_order __m) noexcept
  { __atomic_thread_fence(__m); }

  /// kill_dependency
  template<typename _Tp>
    inline _Tp
    kill_dependency(_Tp __y) noexcept
    {
      _Tp __ret(__y);
      return __ret;
    }


  // Base types for atomics.
  template<typename _IntTp>
    struct __atomic_base;

  /// atomic_char
  typedef __atomic_base<char>               atomic_char;

  /// atomic_schar
  typedef __atomic_base<signed char>            atomic_schar;

  /// atomic_uchar
  typedef __atomic_base<unsigned char>      atomic_uchar;

  /// atomic_short
  typedef __atomic_base<short>          atomic_short;

  /// atomic_ushort
  typedef __atomic_base<unsigned short>     atomic_ushort;

  /// atomic_int
  typedef __atomic_base<int>                atomic_int;

  /// atomic_uint
  typedef __atomic_base<unsigned int>           atomic_uint;

  /// atomic_long
  typedef __atomic_base<long>               atomic_long;

  /// atomic_ulong
  typedef __atomic_base<unsigned long>      atomic_ulong;

  /// atomic_llong
  typedef __atomic_base<long long>          atomic_llong;

  /// atomic_ullong
  typedef __atomic_base<unsigned long long>     atomic_ullong;

  /// atomic_wchar_t
  typedef __atomic_base<wchar_t>        atomic_wchar_t;

  /// atomic_char16_t
  typedef __atomic_base<char16_t>       atomic_char16_t;

  /// atomic_char32_t
  typedef __atomic_base<char32_t>       atomic_char32_t;

  /// atomic_char32_t
  typedef __atomic_base<char32_t>       atomic_char32_t;


  /// atomic_int_least8_t
  typedef __atomic_base<int_least8_t>       atomic_int_least8_t;

  /// atomic_uint_least8_t
  typedef __atomic_base<uint_least8_t>          atomic_uint_least8_t;

  /// atomic_int_least16_t
  typedef __atomic_base<int_least16_t>          atomic_int_least16_t;

  /// atomic_uint_least16_t
  typedef __atomic_base<uint_least16_t>         atomic_uint_least16_t;

  /// atomic_int_least32_t
  typedef __atomic_base<int_least32_t>          atomic_int_least32_t;

  /// atomic_uint_least32_t
  typedef __atomic_base<uint_least32_t>         atomic_uint_least32_t;

  /// atomic_int_least64_t
  typedef __atomic_base<int_least64_t>          atomic_int_least64_t;

  /// atomic_uint_least64_t
  typedef __atomic_base<uint_least64_t>         atomic_uint_least64_t;


  /// atomic_int_fast8_t
  typedef __atomic_base<int_fast8_t>        atomic_int_fast8_t;

  /// atomic_uint_fast8_t
  typedef __atomic_base<uint_fast8_t>           atomic_uint_fast8_t;

  /// atomic_int_fast16_t
  typedef __atomic_base<int_fast16_t>           atomic_int_fast16_t;

  /// atomic_uint_fast16_t
  typedef __atomic_base<uint_fast16_t>          atomic_uint_fast16_t;

  /// atomic_int_fast32_t
  typedef __atomic_base<int_fast32_t>           atomic_int_fast32_t;

  /// atomic_uint_fast32_t
  typedef __atomic_base<uint_fast32_t>          atomic_uint_fast32_t;

  /// atomic_int_fast64_t
  typedef __atomic_base<int_fast64_t>           atomic_int_fast64_t;

  /// atomic_uint_fast64_t
  typedef __atomic_base<uint_fast64_t>          atomic_uint_fast64_t;


  /// atomic_intptr_t
  typedef __atomic_base<intptr_t>           atomic_intptr_t;

  /// atomic_uintptr_t
  typedef __atomic_base<uintptr_t>              atomic_uintptr_t;

  /// atomic_size_t
  typedef __atomic_base<size_t>             atomic_size_t;

  /// atomic_intmax_t
  typedef __atomic_base<intmax_t>           atomic_intmax_t;

  /// atomic_uintmax_t
  typedef __atomic_base<uintmax_t>              atomic_uintmax_t;

  /// atomic_ptrdiff_t
  typedef __atomic_base<ptrdiff_t>              atomic_ptrdiff_t;


#define ATOMIC_VAR_INIT(_VI) { _VI }

  template<typename _Tp>
    struct atomic;

  template<typename _Tp>
    struct atomic<_Tp*>;


  /**
   *  @brief Base type for atomic_flag.
   *
   *  Base type is POD with data, allowing atomic_flag to derive from
   *  it and meet the standard layout type requirement. In addition to
   *  compatibilty with a C interface, this allows different
   *  implementations of atomic_flag to use the same atomic operation
   *  functions, via a standard conversion to the __atomic_flag_base
   *  argument.
  */
  _GLIBCXX_BEGIN_EXTERN_C

  struct __atomic_flag_base
  {
    /* The target's "set" value for test-and-set may not be exactly 1.  */
#if __GCC_ATOMIC_TEST_AND_SET_TRUEVAL == 1
    bool _M_i;
#else
    unsigned char _M_i;
#endif
  };

  _GLIBCXX_END_EXTERN_C

#define ATOMIC_FLAG_INIT { 0 }

  /// atomic_flag
  struct atomic_flag : public __atomic_flag_base
  {
    atomic_flag() noexcept = default;
    ~atomic_flag() noexcept = default;
    atomic_flag(const atomic_flag&) = delete;
    atomic_flag& operator=(const atomic_flag&) = delete;
    atomic_flag& operator=(const atomic_flag&) volatile = delete;

    // Conversion to ATOMIC_FLAG_INIT.
    constexpr atomic_flag(bool __i) noexcept
      : __atomic_flag_base({ __i ? __GCC_ATOMIC_TEST_AND_SET_TRUEVAL : 0 })
    { }

    bool
    test_and_set(memory_order __m = memory_order_seq_cst) noexcept
    {
      return __atomic_test_and_set (&_M_i, __m);
    }

    bool
    test_and_set(memory_order __m = memory_order_seq_cst) volatile noexcept
    {
      return __atomic_test_and_set (&_M_i, __m);
    }

    void
    clear(memory_order __m = memory_order_seq_cst) noexcept
    {
      __glibcxx_assert(__m != memory_order_consume);
      __glibcxx_assert(__m != memory_order_acquire);
      __glibcxx_assert(__m != memory_order_acq_rel);

      __atomic_clear (&_M_i, __m);
    }

    void
    clear(memory_order __m = memory_order_seq_cst) volatile noexcept
    {
      __glibcxx_assert(__m != memory_order_consume);
      __glibcxx_assert(__m != memory_order_acquire);
      __glibcxx_assert(__m != memory_order_acq_rel);

      __atomic_clear (&_M_i, __m);
    }
  };


  /// Base class for atomic integrals.
  //
  // For each of the integral types, define atomic_[integral type] struct
  //
  // atomic_bool     bool
  // atomic_char     char
  // atomic_schar    signed char
  // atomic_uchar    unsigned char
  // atomic_short    short
  // atomic_ushort   unsigned short
  // atomic_int      int
  // atomic_uint     unsigned int
  // atomic_long     long
  // atomic_ulong    unsigned long
  // atomic_llong    long long
  // atomic_ullong   unsigned long long
  // atomic_char16_t char16_t
  // atomic_char32_t char32_t
  // atomic_wchar_t  wchar_t
  //
  // NB: Assuming _ITp is an integral scalar type that is 1, 2, 4, or
  // 8 bytes, since that is what GCC built-in functions for atomic
  // memory access expect.
  template<typename _ITp>
    struct __atomic_base
    {
    private:
      typedef _ITp  __int_type;

      __int_type    _M_i;

    public:
      __atomic_base() noexcept = default;
      ~__atomic_base() noexcept = default;
      __atomic_base(const __atomic_base&) = delete;
      __atomic_base& operator=(const __atomic_base&) = delete;
      __atomic_base& operator=(const __atomic_base&) volatile = delete;

      // Requires __int_type convertible to _M_i.
      constexpr __atomic_base(__int_type __i) noexcept : _M_i (__i) { }

      operator __int_type() const noexcept
      { return load(); }

      operator __int_type() const volatile noexcept
      { return load(); }

      __int_type
      operator=(__int_type __i) noexcept
      {
    store(__i);
    return __i;
      }

      __int_type
      operator=(__int_type __i) volatile noexcept
      {
    store(__i);
    return __i;
      }

      __int_type
      operator++(int) noexcept
      { return fetch_add(1); }

      __int_type
      operator++(int) volatile noexcept
      { return fetch_add(1); }

      __int_type
      operator--(int) noexcept
      { return fetch_sub(1); }

      __int_type
      operator--(int) volatile noexcept
      { return fetch_sub(1); }

      __int_type
      operator++() noexcept
      { return __atomic_add_fetch(&_M_i, 1, memory_order_seq_cst); }

      __int_type
      operator++() volatile noexcept
      { return __atomic_add_fetch(&_M_i, 1, memory_order_seq_cst); }

      __int_type
      operator--() noexcept
      { return __atomic_sub_fetch(&_M_i, 1, memory_order_seq_cst); }

      __int_type
      operator--() volatile noexcept
      { return __atomic_sub_fetch(&_M_i, 1, memory_order_seq_cst); }

      __int_type
      operator+=(__int_type __i) noexcept
      { return __atomic_add_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator+=(__int_type __i) volatile noexcept
      { return __atomic_add_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator-=(__int_type __i) noexcept
      { return __atomic_sub_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator-=(__int_type __i) volatile noexcept
      { return __atomic_sub_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator&=(__int_type __i) noexcept
      { return __atomic_and_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator&=(__int_type __i) volatile noexcept
      { return __atomic_and_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator|=(__int_type __i) noexcept
      { return __atomic_or_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator|=(__int_type __i) volatile noexcept
      { return __atomic_or_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator^=(__int_type __i) noexcept
      { return __atomic_xor_fetch(&_M_i, __i, memory_order_seq_cst); }

      __int_type
      operator^=(__int_type __i) volatile noexcept
      { return __atomic_xor_fetch(&_M_i, __i, memory_order_seq_cst); }

      bool
      is_lock_free() const noexcept
      { return __atomic_is_lock_free (sizeof (_M_i), &_M_i); }

      bool
      is_lock_free() const volatile noexcept
      { return __atomic_is_lock_free (sizeof (_M_i), &_M_i); }

      void
      store(__int_type __i, memory_order __m = memory_order_seq_cst) noexcept
      {
    __glibcxx_assert(__m != memory_order_acquire);
    __glibcxx_assert(__m != memory_order_acq_rel);
    __glibcxx_assert(__m != memory_order_consume);

    __atomic_store_n(&_M_i, __i, __m);
      }

      void
      store(__int_type __i,
        memory_order __m = memory_order_seq_cst) volatile noexcept
      {
    __glibcxx_assert(__m != memory_order_acquire);
    __glibcxx_assert(__m != memory_order_acq_rel);
    __glibcxx_assert(__m != memory_order_consume);

    __atomic_store_n(&_M_i, __i, __m);
      }

      __int_type
      load(memory_order __m = memory_order_seq_cst) const noexcept
      {
    __glibcxx_assert(__m != memory_order_release);
    __glibcxx_assert(__m != memory_order_acq_rel);

    return __atomic_load_n(&_M_i, __m);
      }

      __int_type
      load(memory_order __m = memory_order_seq_cst) const volatile noexcept
      {
    __glibcxx_assert(__m != memory_order_release);
    __glibcxx_assert(__m != memory_order_acq_rel);

    return __atomic_load_n(&_M_i, __m);
      }

      __int_type
      exchange(__int_type __i,
           memory_order __m = memory_order_seq_cst) noexcept
      {
    return __atomic_exchange_n(&_M_i, __i, __m);
      }


      __int_type
      exchange(__int_type __i,
           memory_order __m = memory_order_seq_cst) volatile noexcept
      {
    return __atomic_exchange_n(&_M_i, __i, __m);
      }

      bool
      compare_exchange_weak(__int_type& __i1, __int_type __i2,
                memory_order __m1, memory_order __m2) noexcept
      {
    __glibcxx_assert(__m2 != memory_order_release);
    __glibcxx_assert(__m2 != memory_order_acq_rel);
    __glibcxx_assert(__m2 <= __m1);

    return __atomic_compare_exchange_n(&_M_i, &__i1, __i2, 1, __m1, __m2);
      }

      bool
      compare_exchange_weak(__int_type& __i1, __int_type __i2,
                memory_order __m1,
                memory_order __m2) volatile noexcept
      {
    __glibcxx_assert(__m2 != memory_order_release);
    __glibcxx_assert(__m2 != memory_order_acq_rel);
    __glibcxx_assert(__m2 <= __m1);

    return __atomic_compare_exchange_n(&_M_i, &__i1, __i2, 1, __m1, __m2);
      }

      bool
      compare_exchange_weak(__int_type& __i1, __int_type __i2,
                memory_order __m = memory_order_seq_cst) noexcept
      {
    return compare_exchange_weak(__i1, __i2, __m,
                     __cmpexch_failure_order(__m));
      }

      bool
      compare_exchange_weak(__int_type& __i1, __int_type __i2,
           memory_order __m = memory_order_seq_cst) volatile noexcept
      {
    return compare_exchange_weak(__i1, __i2, __m,
                     __cmpexch_failure_order(__m));
      }

      bool
      compare_exchange_strong(__int_type& __i1, __int_type __i2,
                  memory_order __m1, memory_order __m2) noexcept
      {
    __glibcxx_assert(__m2 != memory_order_release);
    __glibcxx_assert(__m2 != memory_order_acq_rel);
    __glibcxx_assert(__m2 <= __m1);

    return __atomic_compare_exchange_n(&_M_i, &__i1, __i2, 0, __m1, __m2);
      }

      bool
      compare_exchange_strong(__int_type& __i1, __int_type __i2,
                  memory_order __m1,
                  memory_order __m2) volatile noexcept
      {
    __glibcxx_assert(__m2 != memory_order_release);
    __glibcxx_assert(__m2 != memory_order_acq_rel);
    __glibcxx_assert(__m2 <= __m1);

    return __atomic_compare_exchange_n(&_M_i, &__i1, __i2, 0, __m1, __m2);
      }

      bool
      compare_exchange_strong(__int_type& __i1, __int_type __i2,
                  memory_order __m = memory_order_seq_cst) noexcept
      {
    return compare_exchange_strong(__i1, __i2, __m,
                       __cmpexch_failure_order(__m));
      }

      bool
      compare_exchange_strong(__int_type& __i1, __int_type __i2,
         memory_order __m = memory_order_seq_cst) volatile noexcept
      {
    return compare_exchange_strong(__i1, __i2, __m,
                       __cmpexch_failure_order(__m));
      }

      __int_type
      fetch_add(__int_type __i,
        memory_order __m = memory_order_seq_cst) noexcept
      { return __atomic_fetch_add(&_M_i, __i, __m); }

      __int_type
      fetch_add(__int_type __i,
        memory_order __m = memory_order_seq_cst) volatile noexcept
      { return __atomic_fetch_add(&_M_i, __i, __m); }

      __int_type
      fetch_sub(__int_type __i,
        memory_order __m = memory_order_seq_cst) noexcept
      { return __atomic_fetch_sub(&_M_i, __i, __m); }

      __int_type
      fetch_sub(__int_type __i,
        memory_order __m = memory_order_seq_cst) volatile noexcept
      { return __atomic_fetch_sub(&_M_i, __i, __m); }

      __int_type
      fetch_and(__int_type __i,
        memory_order __m = memory_order_seq_cst) noexcept
      { return __atomic_fetch_and(&_M_i, __i, __m); }

      __int_type
      fetch_and(__int_type __i,
        memory_order __m = memory_order_seq_cst) volatile noexcept
      { return __atomic_fetch_and(&_M_i, __i, __m); }

      __int_type
      fetch_or(__int_type __i,
           memory_order __m = memory_order_seq_cst) noexcept
      { return __atomic_fetch_or(&_M_i, __i, __m); }

      __int_type
      fetch_or(__int_type __i,
           memory_order __m = memory_order_seq_cst) volatile noexcept
      { return __atomic_fetch_or(&_M_i, __i, __m); }

      __int_type
      fetch_xor(__int_type __i,
        memory_order __m = memory_order_seq_cst) noexcept
      { return __atomic_fetch_xor(&_M_i, __i, __m); }

      __int_type
      fetch_xor(__int_type __i,
        memory_order __m = memory_order_seq_cst) volatile noexcept
      { return __atomic_fetch_xor(&_M_i, __i, __m); }
    };


  /// Partial specialization for pointer types.
  template<typename _PTp>
    struct __atomic_base<_PTp*>
    {
    private:
      typedef _PTp*     __pointer_type;

      __pointer_type    _M_p;

      // Factored out to facilitate explicit specialization.
      constexpr ptrdiff_t
      _M_type_size(ptrdiff_t __d) { return __d * sizeof(_PTp); }

      constexpr ptrdiff_t
      _M_type_size(ptrdiff_t __d) volatile { return __d * sizeof(_PTp); }

    public:
      __atomic_base() noexcept = default;
      ~__atomic_base() noexcept = default;
      __atomic_base(const __atomic_base&) = delete;
      __atomic_base& operator=(const __atomic_base&) = delete;
      __atomic_base& operator=(const __atomic_base&) volatile = delete;

      // Requires __pointer_type convertible to _M_p.
      constexpr __atomic_base(__pointer_type __p) noexcept : _M_p (__p) { }

      operator __pointer_type() const noexcept
      { return load(); }

      operator __pointer_type() const volatile noexcept
      { return load(); }

      __pointer_type
      operator=(__pointer_type __p) noexcept
      {
    store(__p);
    return __p;
      }

      __pointer_type
      operator=(__pointer_type __p) volatile noexcept
      {
    store(__p);
    return __p;
      }

      __pointer_type
      operator++(int) noexcept
      { return fetch_add(1); }

      __pointer_type
      operator++(int) volatile noexcept
      { return fetch_add(1); }

      __pointer_type
      operator--(int) noexcept
      { return fetch_sub(1); }

      __pointer_type
      operator--(int) volatile noexcept
      { return fetch_sub(1); }

      __pointer_type
      operator++() noexcept
      { return __atomic_add_fetch(&_M_p, _M_type_size(1),
                  memory_order_seq_cst); }

      __pointer_type
      operator++() volatile noexcept
      { return __atomic_add_fetch(&_M_p, _M_type_size(1),
                  memory_order_seq_cst); }

      __pointer_type
      operator--() noexcept
      { return __atomic_sub_fetch(&_M_p, _M_type_size(1),
                  memory_order_seq_cst); }

      __pointer_type
      operator--() volatile noexcept
      { return __atomic_sub_fetch(&_M_p, _M_type_size(1),
                  memory_order_seq_cst); }

      __pointer_type
      operator+=(ptrdiff_t __d) noexcept
      { return __atomic_add_fetch(&_M_p, _M_type_size(__d),
                  memory_order_seq_cst); }

      __pointer_type
      operator+=(ptrdiff_t __d) volatile noexcept
      { return __atomic_add_fetch(&_M_p, _M_type_size(__d),
                  memory_order_seq_cst); }

      __pointer_type
      operator-=(ptrdiff_t __d) noexcept
      { return __atomic_sub_fetch(&_M_p, _M_type_size(__d),
                  memory_order_seq_cst); }

      __pointer_type
      operator-=(ptrdiff_t __d) volatile noexcept
      { return __atomic_sub_fetch(&_M_p, _M_type_size(__d),
                  memory_order_seq_cst); }

      bool
      is_lock_free() const noexcept
      { return __atomic_is_lock_free(_M_type_size(1), &_M_p); }

      bool
      is_lock_free() const volatile noexcept
      { return __atomic_is_lock_free(_M_type_size(1), &_M_p); }

      void
      store(__pointer_type __p,
        memory_order __m = memory_order_seq_cst) noexcept
      {
    __glibcxx_assert(__m != memory_order_acquire);
    __glibcxx_assert(__m != memory_order_acq_rel);
    __glibcxx_assert(__m != memory_order_consume);

    __atomic_store_n(&_M_p, __p, __m);
      }

      void
      store(__pointer_type __p,
        memory_order __m = memory_order_seq_cst) volatile noexcept
      {
    __glibcxx_assert(__m != memory_order_acquire);
    __glibcxx_assert(__m != memory_order_acq_rel);
    __glibcxx_assert(__m != memory_order_consume);

    __atomic_store_n(&_M_p, __p, __m);
      }

      __pointer_type
      load(memory_order __m = memory_order_seq_cst) const noexcept
      {
    __glibcxx_assert(__m != memory_order_release);
    __glibcxx_assert(__m != memory_order_acq_rel);

    return __atomic_load_n(&_M_p, __m);
      }

      __pointer_type
      load(memory_order __m = memory_order_seq_cst) const volatile noexcept
      {
    __glibcxx_assert(__m != memory_order_release);
    __glibcxx_assert(__m != memory_order_acq_rel);

    return __atomic_load_n(&_M_p, __m);
      }

      __pointer_type
      exchange(__pointer_type __p,
           memory_order __m = memory_order_seq_cst) noexcept
      {
    return __atomic_exchange_n(&_M_p, __p, __m);
      }


      __pointer_type
      exchange(__pointer_type __p,
           memory_order __m = memory_order_seq_cst) volatile noexcept
      {
    return __atomic_exchange_n(&_M_p, __p, __m);
      }

      bool
      compare_exchange_strong(__pointer_type& __p1, __pointer_type __p2,
                  memory_order __m1,
                  memory_order __m2) noexcept
      {
    __glibcxx_assert(__m2 != memory_order_release);
    __glibcxx_assert(__m2 != memory_order_acq_rel);
    __glibcxx_assert(__m2 <= __m1);

    return __atomic_compare_exchange_n(&_M_p, &__p1, __p2, 0, __m1, __m2);
      }

      bool
      compare_exchange_strong(__pointer_type& __p1, __pointer_type __p2,
                  memory_order __m1,
                  memory_order __m2) volatile noexcept
      {
    __glibcxx_assert(__m2 != memory_order_release);
    __glibcxx_assert(__m2 != memory_order_acq_rel);
    __glibcxx_assert(__m2 <= __m1);

    return __atomic_compare_exchange_n(&_M_p, &__p1, __p2, 0, __m1, __m2);
      }

      __pointer_type
      fetch_add(ptrdiff_t __d,
        memory_order __m = memory_order_seq_cst) noexcept
      { return __atomic_fetch_add(&_M_p, _M_type_size(__d), __m); }

      __pointer_type
      fetch_add(ptrdiff_t __d,
        memory_order __m = memory_order_seq_cst) volatile noexcept
      { return __atomic_fetch_add(&_M_p, _M_type_size(__d), __m); }

      __pointer_type
      fetch_sub(ptrdiff_t __d,
        memory_order __m = memory_order_seq_cst) noexcept
      { return __atomic_fetch_sub(&_M_p, _M_type_size(__d), __m); }

      __pointer_type
      fetch_sub(ptrdiff_t __d,
        memory_order __m = memory_order_seq_cst) volatile noexcept
      { return __atomic_fetch_sub(&_M_p, _M_type_size(__d), __m); }
    };

  // @} group atomics

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

#endif