text: // Aligned memory buffer -*- C++ -*-
  
  // Copyright (C) 2013-2020 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 ext/aligned_buffer.h
   *  This file is a GNU extension to the Standard C++ Library.
   */
  
  #ifndef _ALIGNED_BUFFER_H
  #define _ALIGNED_BUFFER_H 1
  
  #pragma GCC system_header
  
  #if __cplusplus >= 201103L
  # include <type_traits>
  #else
  # include <bits/c++0x_warning.h>
  #endif
  
  namespace __gnu_cxx
  {
    // A utility type containing a POD object that can hold an object of type
    // _Tp initialized via placement new or allocator_traits::construct.
    // Intended for use as a data member subobject, use __aligned_buffer for
    // complete objects.
    template<typename _Tp>
      struct __aligned_membuf
      {
        // Target macro ADJUST_FIELD_ALIGN can produce different alignment for
        // types when used as class members. __aligned_membuf is intended
        // for use as a class member, so align the buffer as for a class member.
        // Since GCC 8 we could just use alignof(_Tp) instead, but older
        // versions of non-GNU compilers might still need this trick.
        struct _Tp2 { _Tp _M_t; };
  
        alignas(__alignof__(_Tp2::_M_t)) unsigned char _M_storage[sizeof(_Tp)];
  
        __aligned_membuf() = default;
  
        // Can be used to avoid value-initialization zeroing _M_storage.
        __aligned_membuf(std::nullptr_t) { }
  
        void*
        _M_addr() noexcept
        { return static_cast<void*>(&_M_storage); }
  
        const void*
        _M_addr() const noexcept
        { return static_cast<const void*>(&_M_storage); }
  
        _Tp*
        _M_ptr() noexcept
        { return static_cast<_Tp*>(_M_addr()); }
  
        const _Tp*
        _M_ptr() const noexcept
        { return static_cast<const _Tp*>(_M_addr()); }
      };
  
  #if _GLIBCXX_INLINE_VERSION
    template<typename _Tp>
      using __aligned_buffer = __aligned_membuf<_Tp>;
  #else
    // Similar to __aligned_membuf but aligned for complete objects, not members.
    // This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h>
    // and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf
    // instead, as it has smaller size for some types on some targets.
    // This type is still used to avoid an ABI change.
    template<typename _Tp>
      struct __aligned_buffer
      : std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>
      {
        typename
  	std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>::type _M_storage;
  
        __aligned_buffer() = default;
  
        // Can be used to avoid value-initialization
        __aligned_buffer(std::nullptr_t) { }
  
        void*
        _M_addr() noexcept
        {
          return static_cast<void*>(&_M_storage);
        }
  
        const void*
        _M_addr() const noexcept
        {
          return static_cast<const void*>(&_M_storage);
        }
  
        _Tp*
        _M_ptr() noexcept
        { return static_cast<_Tp*>(_M_addr()); }
  
        const _Tp*
        _M_ptr() const noexcept
        { return static_cast<const _Tp*>(_M_addr()); }
      };
  #endif
  
  } // namespace
  
  #endif /* _ALIGNED_BUFFER_H */
  