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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 */
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