1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
|
// Aligned memory buffer -*- C++ -*-
// Copyright (C) 2013-2014 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file ext/aligned_buffer.h
* This file is a GNU extension to the Standard C++ Library.
*/
#ifndef _ALIGNED_BUFFER_H
#define _ALIGNED_BUFFER_H 1
#pragma GCC system_header
#if __cplusplus >= 201103L
# include <type_traits>
#else
# include <bits/c++0x_warning.h>
#endif
namespace __gnu_cxx
{
// A utility type containing a POD object that can hold an object of type
// _Tp initialized via placement new or allocator_traits::construct.
// Intended for use as a data member subobject, use __aligned_buffer for
// complete objects.
template<typename _Tp>
struct __aligned_membuf
{
// Target macro ADJUST_FIELD_ALIGN can produce different alignment for
// types when used as class members. __aligned_membuf is intended
// for use as a class member, so align the buffer as for a class member.
struct _Tp2 { _Tp _M_t; };
alignas(__alignof__(_Tp2::_M_t)) unsigned char _M_storage[sizeof(_Tp)];
__aligned_membuf() = default;
// Can be used to avoid value-initialization zeroing _M_storage.
__aligned_membuf(std::nullptr_t) { }
void*
_M_addr() noexcept
{ return static_cast<void*>(&_M_storage); }
const void*
_M_addr() const noexcept
{ return static_cast<const void*>(&_M_storage); }
_Tp*
_M_ptr() noexcept
{ return static_cast<_Tp*>(_M_addr()); }
const _Tp*
_M_ptr() const noexcept
{ return static_cast<const _Tp*>(_M_addr()); }
};
// Similar to __aligned_membuf but aligned for complete objects, not members.
// This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h>
// and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf
// instead, as it has smaller size for some types on some targets.
// This type is still used to avoid an ABI change.
template<typename _Tp>
struct __aligned_buffer
: std::aligned_storage<sizeof(_Tp), std::alignment_of<_Tp>::value>
{
typename
std::aligned_storage<sizeof(_Tp), std::alignment_of<_Tp>::value>::type
_M_storage;
void*
_M_addr() noexcept
{
return static_cast<void*>(&_M_storage);
}
const void*
_M_addr() const noexcept
{
return static_cast<const void*>(&_M_storage);
}
_Tp*
_M_ptr() noexcept
{ return static_cast<_Tp*>(_M_addr()); }
const _Tp*
_M_ptr() const noexcept
{ return static_cast<const _Tp*>(_M_addr()); }
};
} // namespace
#endif /* _ALIGNED_BUFFER_H */
|
