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       1             : // Aligned memory buffer -*- C++ -*-
       2             : 
       3             : // Copyright (C) 2013-2016 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             :       struct _Tp2 { _Tp _M_t; };
      53             : 
      54             :       alignas(__alignof__(_Tp2::_M_t)) unsigned char _M_storage[sizeof(_Tp)];
      55             : 
      56           0 :       __aligned_membuf() = default;
      57             : 
      58             :       // Can be used to avoid value-initialization zeroing _M_storage.
      59             :       __aligned_membuf(std::nullptr_t) { }
      60             : 
      61             :       void*
      62           0 :       _M_addr() noexcept
      63           0 :       { return static_cast<void*>(&_M_storage); }
      64             : 
      65             :       const void*
      66           0 :       _M_addr() const noexcept
      67           0 :       { return static_cast<const void*>(&_M_storage); }
      68             : 
      69             :       _Tp*
      70           0 :       _M_ptr() noexcept
      71           0 :       { return static_cast<_Tp*>(_M_addr()); }
      72             : 
      73             :       const _Tp*
      74           0 :       _M_ptr() const noexcept
      75           0 :       { return static_cast<const _Tp*>(_M_addr()); }
      76             :     };
      77             : 
      78             :   // Similar to __aligned_membuf but aligned for complete objects, not members.
      79             :   // This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h>
      80             :   // and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf
      81             :   // instead, as it has smaller size for some types on some targets.
      82             :   // This type is still used to avoid an ABI change.
      83             :   template<typename _Tp>
      84             :     struct __aligned_buffer
      85             :     : std::aligned_storage<sizeof(_Tp), std::alignment_of<_Tp>::value>
      86             :     {
      87             :       typename
      88             :         std::aligned_storage<sizeof(_Tp), std::alignment_of<_Tp>::value>::type
      89             :         _M_storage;
      90             : 
      91             :       __aligned_buffer() = default;
      92             : 
      93             :       // Can be used to avoid value-initialization
      94             :       __aligned_buffer(std::nullptr_t) { }
      95             : 
      96             :       void*
      97             :       _M_addr() noexcept
      98             :       {
      99             :         return static_cast<void*>(&_M_storage);
     100             :       }
     101             : 
     102             :       const void*
     103             :       _M_addr() const noexcept
     104             :       {
     105             :         return static_cast<const void*>(&_M_storage);
     106             :       }
     107             : 
     108             :       _Tp*
     109             :       _M_ptr() noexcept
     110             :       { return static_cast<_Tp*>(_M_addr()); }
     111             : 
     112             :       const _Tp*
     113             :       _M_ptr() const noexcept
     114             :       { return static_cast<const _Tp*>(_M_addr()); }
     115             :     };
     116             : 
     117             : } // namespace
     118             : 
     119             : #endif /* _ALIGNED_BUFFER_H */