1 | // Aligned memory buffer -*- C++ -*- |
2 | |
3 | // Copyright (C) 2013-2019 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 | // 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. |
89 | template<typename _Tp> |
90 | struct __aligned_buffer |
91 | : std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)> |
92 | { |
93 | typename |
94 | std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>::type _M_storage; |
95 | |
96 | __aligned_buffer() = default; |
97 | |
98 | // Can be used to avoid value-initialization |
99 | __aligned_buffer(std::nullptr_t) { } |
100 | |
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 | }; |
121 | #endif |
122 | |
123 | } // namespace |
124 | |
125 | #endif /* _ALIGNED_BUFFER_H */ |
126 | |