| // Aligned memory buffer -*- C++ -*- |
| |
| // Copyright (C) 2013-2020 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. |
| // Since GCC 8 we could just use alignof(_Tp) instead, but older |
| // versions of non-GNU compilers might still need this trick. |
| 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()); } |
| }; |
| |
| #if _GLIBCXX_INLINE_VERSION |
| template<typename _Tp> |
| using __aligned_buffer = __aligned_membuf<_Tp>; |
| #else |
| // 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), __alignof__(_Tp)> |
| { |
| typename |
| std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>::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()); } |
| }; |
| #endif |
| |
| } // namespace |
| |
| #endif /* _ALIGNED_BUFFER_H */ |