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1 | // Aligned memory buffer -*- C++ -*- |
2 | ||
99dee823 | 3 | // Copyright (C) 2013-2021 Free Software Foundation, Inc. |
f2e2de5f JW |
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 | { | |
2097b5b0 JW |
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. | |
8c9b3852 JW |
52 | // Since GCC 8 we could just use alignof(_Tp) instead, but older |
53 | // versions of non-GNU compilers might still need this trick. | |
2097b5b0 JW |
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 | ||
549b1796 FD |
80 | #if _GLIBCXX_INLINE_VERSION |
81 | template<typename _Tp> | |
82 | using __aligned_buffer = __aligned_membuf<_Tp>; | |
83 | #else | |
2097b5b0 JW |
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. | |
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89 | template<typename _Tp> |
90 | struct __aligned_buffer | |
8c9b3852 | 91 | : std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)> |
f2e2de5f JW |
92 | { |
93 | typename | |
8c9b3852 | 94 | std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>::type _M_storage; |
f2e2de5f | 95 | |
e8043fa6 JW |
96 | __aligned_buffer() = default; |
97 | ||
98 | // Can be used to avoid value-initialization | |
99 | __aligned_buffer(std::nullptr_t) { } | |
100 | ||
f2e2de5f JW |
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 | }; | |
549b1796 | 121 | #endif |
f2e2de5f JW |
122 | |
123 | } // namespace | |
124 | ||
125 | #endif /* _ALIGNED_BUFFER_H */ |