120 lines
3.7 KiB
C++
120 lines
3.7 KiB
C++
// Aligned memory buffer -*- C++ -*-
|
|
|
|
// Copyright (C) 2013-2016 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;
|
|
|
|
__aligned_buffer() = default;
|
|
|
|
// Can be used to avoid value-initialization
|
|
__aligned_buffer(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()); }
|
|
};
|
|
|
|
} // namespace
|
|
|
|
#endif /* _ALIGNED_BUFFER_H */
|