// Aligned memory buffer -*- C++ -*-
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// Copyright (C) 2013-2020 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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// 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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// 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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// 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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/** @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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#ifndef _ALIGNED_BUFFER_H
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#define _ALIGNED_BUFFER_H 1
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#pragma GCC system_header
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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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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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alignas(__alignof__(_Tp2::_M_t)) unsigned char _M_storage[sizeof(_Tp)];
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__aligned_membuf() = default;
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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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void*
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_M_addr() noexcept
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{ return static_cast<void*>(&_M_storage); }
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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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_Tp*
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_M_ptr() noexcept
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{ return static_cast<_Tp*>(_M_addr()); }
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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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#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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__aligned_buffer() = default;
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// Can be used to avoid value-initialization
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__aligned_buffer(std::nullptr_t) { }
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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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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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_Tp*
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_M_ptr() noexcept
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{ return static_cast<_Tp*>(_M_addr()); }
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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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} // namespace
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#endif /* _ALIGNED_BUFFER_H */
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