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1 : : // Aligned memory buffer -*- C++ -*-
2 : :
3 : : // Copyright (C) 2013-2015 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 : : __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 : : _M_addr() noexcept
63 : 0 : { return static_cast<void*>(&_M_storage); }
64 : :
65 : : const void*
66 : : _M_addr() const noexcept
67 : : { return static_cast<const void*>(&_M_storage); }
68 : :
69 : : _Tp*
70 : : _M_ptr() noexcept
71 : : { return static_cast<_Tp*>(_M_addr()); }
72 : :
73 : : const _Tp*
74 : : _M_ptr() const noexcept
75 : : { 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 */
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