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// Aligned memory buffer -*- C++ -*- |
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// Copyright (C) 2013-2021 Free Software Foundation, Inc. |
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// |
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// This file is part of the GNU ISO C++ Library. This library is free |
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// software; you can redistribute it and/or modify it under the |
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// terms of the GNU General Public License as published by the |
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// Free Software Foundation; either version 3, or (at your option) |
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// any later version. |
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|
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// This library is distributed in the hope that it will be useful, |
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// but WITHOUT ANY WARRANTY; without even the implied warranty of |
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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// GNU General Public License for more details. |
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|
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// Under Section 7 of GPL version 3, you are granted additional |
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// permissions described in the GCC Runtime Library Exception, version |
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// 3.1, as published by the Free Software Foundation. |
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|
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// You should have received a copy of the GNU General Public License and |
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// a copy of the GCC Runtime Library Exception along with this program; |
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
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// <http://www.gnu.org/licenses/>. |
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|
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/** @file ext/aligned_buffer.h |
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* This file is a GNU extension to the Standard C++ Library. |
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*/ |
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|
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#ifndef _ALIGNED_BUFFER_H |
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#define _ALIGNED_BUFFER_H 1 |
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|
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#pragma GCC system_header |
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|
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#if __cplusplus >= 201103L |
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# include <type_traits> |
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#else |
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# include <bits/c++0x_warning.h> |
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#endif |
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|
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namespace __gnu_cxx |
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{ |
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// A utility type containing a POD object that can hold an object of type |
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// _Tp initialized via placement new or allocator_traits::construct. |
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// Intended for use as a data member subobject, use __aligned_buffer for |
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// complete objects. |
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template<typename _Tp> |
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struct __aligned_membuf |
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{ |
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// Target macro ADJUST_FIELD_ALIGN can produce different alignment for |
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// types when used as class members. __aligned_membuf is intended |
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// for use as a class member, so align the buffer as for a class member. |
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// Since GCC 8 we could just use alignof(_Tp) instead, but older |
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// versions of non-GNU compilers might still need this trick. |
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struct _Tp2 { _Tp _M_t; }; |
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|
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alignas(__alignof__(_Tp2::_M_t)) unsigned char _M_storage[sizeof(_Tp)]; |
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|
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__aligned_membuf() = default; |
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|
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// Can be used to avoid value-initialization zeroing _M_storage. |
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__aligned_membuf(std::nullptr_t) { } |
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|
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void* |
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_M_addr() noexcept |
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{ return static_cast<void*>(&_M_storage); } |
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|
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const void* |
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_M_addr() const noexcept |
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{ return static_cast<const void*>(&_M_storage); } |
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|
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_Tp* |
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_M_ptr() noexcept |
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{ return static_cast<_Tp*>(_M_addr()); } |
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|
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const _Tp* |
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_M_ptr() const noexcept |
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{ return static_cast<const _Tp*>(_M_addr()); } |
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}; |
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|
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#if _GLIBCXX_INLINE_VERSION |
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template<typename _Tp> |
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using __aligned_buffer = __aligned_membuf<_Tp>; |
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#else |
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// Similar to __aligned_membuf but aligned for complete objects, not members. |
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// This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h> |
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// and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf |
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// instead, as it has smaller size for some types on some targets. |
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// This type is still used to avoid an ABI change. |
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template<typename _Tp> |
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struct __aligned_buffer |
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: std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)> |
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{ |
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typename |
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std::aligned_storage<sizeof(_Tp), __alignof__(_Tp)>::type _M_storage; |
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|
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__aligned_buffer() = default; |
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|
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// Can be used to avoid value-initialization |
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__aligned_buffer(std::nullptr_t) { } |
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|
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void* |
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_M_addr() noexcept |
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{ |
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return static_cast<void*>(&_M_storage); |
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} |
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|
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const void* |
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_M_addr() const noexcept |
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{ |
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return static_cast<const void*>(&_M_storage); |
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} |
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|
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_Tp* |
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_M_ptr() noexcept |
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{ return static_cast<_Tp*>(_M_addr()); } |
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|
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const _Tp* |
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_M_ptr() const noexcept |
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{ return static_cast<const _Tp*>(_M_addr()); } |
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}; |
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#endif |
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|
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} // namespace |
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|
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#endif /* _ALIGNED_BUFFER_H */ |
