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The C and C++ Include Header Files

/usr/include/c++/13/ext/aligned_buffer.h


$ cat -n /usr/include/c++/13/ext/aligned_buffer.h

     1	// Aligned memory buffer -*- C++ -*-
     2	
     3	// Copyright (C) 2013-2023 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	      _M_addr() noexcept
    65	      { return static_cast<void*>(&_M_storage); }
    66	
    67	      const void*
    68	      _M_addr() const noexcept
    69	      { return static_cast<const void*>(&_M_storage); }
    70	
    71	      _Tp*
    72	      _M_ptr() noexcept
    73	      { return static_cast<_Tp*>(_M_addr()); }
    74	
    75	      const _Tp*
    76	      _M_ptr() const noexcept
    77	      { 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	#pragma GCC diagnostic push
    85	#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
    86	  // Similar to __aligned_membuf but aligned for complete objects, not members.
    87	  // This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h>
    88	  // and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf
    89	  // instead, as it has smaller size for some types on some targets.
    90	  // This type is still used to avoid an ABI change.
    91	  template<typename _Tp>
    92	    struct __aligned_buffer
    93	    : std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>
    94	    {
    95	      typename
    96		std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>::type _M_storage;
    97	
    98	      __aligned_buffer() = default;
    99	
   100	      // Can be used to avoid value-initialization
   101	      __aligned_buffer(std::nullptr_t) { }
   102	
   103	      void*
   104	      _M_addr() noexcept
   105	      {
   106	        return static_cast<void*>(&_M_storage);
   107	      }
   108	
   109	      const void*
   110	      _M_addr() const noexcept
   111	      {
   112	        return static_cast<const void*>(&_M_storage);
   113	      }
   114	
   115	      _Tp*
   116	      _M_ptr() noexcept
   117	      { return static_cast<_Tp*>(_M_addr()); }
   118	
   119	      const _Tp*
   120	      _M_ptr() const noexcept
   121	      { return static_cast<const _Tp*>(_M_addr()); }
   122	    };
   123	#pragma GCC diagnostic pop
   124	#endif
   125	
   126	} // namespace
   127	
   128	#endif /* _ALIGNED_BUFFER_H */