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// Aligned memory buffer -*- C++ -*-
// Copyright (C) 2013-2025 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
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
#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 can just use alignas(_Tp) to get the right alignment.
#ifdef __EDG__
// The EDG front end does not implement the PR c++/69560 alignof change.
struct _Tp2 { _Tp _M_t; };
alignas(__alignof__(_Tp2::_M_t))
#else
alignas(_Tp)
#endif
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
{
// Using __alignof__ gives the alignment for a complete object.
alignas(__alignof__(_Tp)) unsigned char _M_storage[sizeof(_Tp)];
__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 */
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