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- // align implementation -*- C++ -*-
- // Copyright (C) 2014-2022 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 bits/align.h
- * This is an internal header file, included by other library headers.
- * Do not attempt to use it directly. @headername{memory}
- */
- #ifndef _GLIBCXX_ALIGN_H
- #define _GLIBCXX_ALIGN_H 1
- #include <bits/c++config.h>
- #include <bit> // std::has_single_bit
- #include <stdint.h> // uintptr_t
- #include <debug/assertions.h> // _GLIBCXX_DEBUG_ASSERT
- namespace std _GLIBCXX_VISIBILITY(default)
- {
- _GLIBCXX_BEGIN_NAMESPACE_VERSION
- /**
- * @brief Fit aligned storage in buffer.
- *
- * This function tries to fit @a __size bytes of storage with alignment
- * @a __align into the buffer @a __ptr of size @a __space bytes. If such
- * a buffer fits then @a __ptr is changed to point to the first byte of the
- * aligned storage and @a __space is reduced by the bytes used for alignment.
- *
- * C++11 20.6.5 [ptr.align]
- *
- * @param __align A fundamental or extended alignment value.
- * @param __size Size of the aligned storage required.
- * @param __ptr Pointer to a buffer of @a __space bytes.
- * @param __space Size of the buffer pointed to by @a __ptr.
- * @return the updated pointer if the aligned storage fits, otherwise nullptr.
- *
- * @ingroup memory
- */
- inline void*
- align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept
- {
- if (__space < __size)
- return nullptr;
- const auto __intptr = reinterpret_cast<uintptr_t>(__ptr);
- const auto __aligned = (__intptr - 1u + __align) & -__align;
- const auto __diff = __aligned - __intptr;
- if (__diff > (__space - __size))
- return nullptr;
- else
- {
- __space -= __diff;
- return __ptr = reinterpret_cast<void*>(__aligned);
- }
- }
- #if __cplusplus > 201703L
- #define __cpp_lib_assume_aligned 201811L
- /** @brief Inform the compiler that a pointer is aligned.
- *
- * @tparam _Align An alignment value (i.e. a power of two)
- * @tparam _Tp An object type
- * @param __ptr A pointer that is aligned to _Align
- *
- * C++20 20.10.6 [ptr.align]
- *
- * @ingroup memory
- */
- template<size_t _Align, class _Tp>
- [[nodiscard,__gnu__::__always_inline__]]
- constexpr _Tp*
- assume_aligned(_Tp* __ptr) noexcept
- {
- static_assert(std::has_single_bit(_Align));
- if (std::is_constant_evaluated())
- return __ptr;
- else
- {
- // This function is expected to be used in hot code, where
- // __glibcxx_assert would add unwanted overhead.
- _GLIBCXX_DEBUG_ASSERT((uintptr_t)__ptr % _Align == 0);
- return static_cast<_Tp*>(__builtin_assume_aligned(__ptr, _Align));
- }
- }
- #endif // C++2a
- _GLIBCXX_END_NAMESPACE_VERSION
- } // namespace
- #endif /* _GLIBCXX_ALIGN_H */
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