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       1                 :            : // Aligned memory buffer -*- C++ -*-
       2                 :            : 
       3                 :            : // Copyright (C) 2013-2019 Free Software Foundation, Inc.
       4                 :            : //
       5                 :            : // This file is part of the GNU ISO C++ Library.  This library is free
       6                 :            : // software; you can redistribute it and/or modify it under the
       7                 :            : // terms of the GNU General Public License as published by the
       8                 :            : // Free Software Foundation; either version 3, or (at your option)
       9                 :            : // any later version.
      10                 :            : 
      11                 :            : // This library is distributed in the hope that it will be useful,
      12                 :            : // but WITHOUT ANY WARRANTY; without even the implied warranty of
      13                 :            : // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      14                 :            : // GNU General Public License for more details.
      15                 :            : 
      16                 :            : // Under Section 7 of GPL version 3, you are granted additional
      17                 :            : // permissions described in the GCC Runtime Library Exception, version
      18                 :            : // 3.1, as published by the Free Software Foundation.
      19                 :            : 
      20                 :            : // You should have received a copy of the GNU General Public License and
      21                 :            : // a copy of the GCC Runtime Library Exception along with this program;
      22                 :            : // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
      23                 :            : // <http://www.gnu.org/licenses/>.
      24                 :            : 
      25                 :            : /** @file ext/aligned_buffer.h
      26                 :            :  *  This file is a GNU extension to the Standard C++ Library.
      27                 :            :  */
      28                 :            : 
      29                 :            : #ifndef _ALIGNED_BUFFER_H
      30                 :            : #define _ALIGNED_BUFFER_H 1
      31                 :            : 
      32                 :            : #pragma GCC system_header
      33                 :            : 
      34                 :            : #if __cplusplus >= 201103L
      35                 :            : # include <type_traits>
      36                 :            : #else
      37                 :            : # include <bits/c++0x_warning.h>
      38                 :            : #endif
      39                 :            : 
      40                 :            : namespace __gnu_cxx
      41                 :            : {
      42                 :            :   // A utility type containing a POD object that can hold an object of type
      43                 :            :   // _Tp initialized via placement new or allocator_traits::construct.
      44                 :            :   // Intended for use as a data member subobject, use __aligned_buffer for
      45                 :            :   // complete objects.
      46                 :            :   template<typename _Tp>
      47                 :            :     struct __aligned_membuf
      48                 :            :     {
      49                 :            :       // Target macro ADJUST_FIELD_ALIGN can produce different alignment for
      50                 :            :       // types when used as class members. __aligned_membuf is intended
      51                 :            :       // for use as a class member, so align the buffer as for a class member.
      52                 :            :       // Since GCC 8 we could just use alignof(_Tp) instead, but older
      53                 :            :       // versions of non-GNU compilers might still need this trick.
      54                 :            :       struct _Tp2 { _Tp _M_t; };
      55                 :            : 
      56                 :            :       alignas(__alignof__(_Tp2::_M_t)) unsigned char _M_storage[sizeof(_Tp)];
      57                 :            : 
      58                 :            :       __aligned_membuf() = default;
      59                 :            : 
      60                 :            :       // Can be used to avoid value-initialization zeroing _M_storage.
      61                 :            :       __aligned_membuf(std::nullptr_t) { }
      62                 :            : 
      63                 :            :       void*
      64                 :        233 :       _M_addr() noexcept
      65                 :        233 :       { return static_cast<void*>(&_M_storage); }
      66                 :            : 
      67                 :            :       const void*
      68                 :         45 :       _M_addr() const noexcept
      69                 :         45 :       { return static_cast<const void*>(&_M_storage); }
      70                 :            : 
      71                 :            :       _Tp*
      72                 :        233 :       _M_ptr() noexcept
      73                 :        233 :       { return static_cast<_Tp*>(_M_addr()); }
      74                 :            : 
      75                 :            :       const _Tp*
      76                 :         45 :       _M_ptr() const noexcept
      77                 :         45 :       { return static_cast<const _Tp*>(_M_addr()); }
      78                 :            :     };
      79                 :            : 
      80                 :            : #if _GLIBCXX_INLINE_VERSION
      81                 :            :   template<typename _Tp>
      82                 :            :     using __aligned_buffer = __aligned_membuf<_Tp>;
      83                 :            : #else
      84                 :            :   // Similar to __aligned_membuf but aligned for complete objects, not members.
      85                 :            :   // This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h>
      86                 :            :   // and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf
      87                 :            :   // instead, as it has smaller size for some types on some targets.
      88                 :            :   // This type is still used to avoid an ABI change.
      89                 :            :   template<typename _Tp>
      90                 :            :     struct __aligned_buffer
      91                 :            :     : std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>
      92                 :            :     {
      93                 :            :       typename
      94                 :            :         std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>::type _M_storage;
      95                 :            : 
      96                 :            :       __aligned_buffer() = default;
      97                 :            : 
      98                 :            :       // Can be used to avoid value-initialization
      99                 :            :       __aligned_buffer(std::nullptr_t) { }
     100                 :            : 
     101                 :            :       void*
     102                 :            :       _M_addr() noexcept
     103                 :            :       {
     104                 :            :         return static_cast<void*>(&_M_storage);
     105                 :            :       }
     106                 :            : 
     107                 :            :       const void*
     108                 :            :       _M_addr() const noexcept
     109                 :            :       {
     110                 :            :         return static_cast<const void*>(&_M_storage);
     111                 :            :       }
     112                 :            : 
     113                 :            :       _Tp*
     114                 :            :       _M_ptr() noexcept
     115                 :            :       { return static_cast<_Tp*>(_M_addr()); }
     116                 :            : 
     117                 :            :       const _Tp*
     118                 :            :       _M_ptr() const noexcept
     119                 :            :       { return static_cast<const _Tp*>(_M_addr()); }
     120                 :            :     };
     121                 :            : #endif
     122                 :            : 
     123                 :            : } // namespace
     124                 :            : 
     125                 :            : #endif /* _ALIGNED_BUFFER_H */