libcxx/include/__memory/temporary_buffer.h

// -*- C++ -*-
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP___MEMORY_TEMPORARY_BUFFER_H
#define _LIBCPP___MEMORY_TEMPORARY_BUFFER_H

#include <__config>
#include <cstddef>
#include <new>
#include <utility> // pair

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

template <class _Tp>
_LIBCPP_NODISCARD_EXT _LIBCPP_NO_CFI
pair<_Tp*, ptrdiff_t>
get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT
{
    pair<_Tp*, ptrdiff_t> __r(0, 0);
    const ptrdiff_t __m = (~ptrdiff_t(0) ^
                           ptrdiff_t(ptrdiff_t(1) << (sizeof(ptrdiff_t) * __CHAR_BIT__ - 1)))
                           / sizeof(_Tp);
    if (__n > __m)
        __n = __m;
    while (__n > 0)
    {
#if !defined(_LIBCPP_HAS_NO_ALIGNED_ALLOCATION)
    if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp)))
        {
            align_val_t __al =
                align_val_t(alignment_of<_Tp>::value);
            __r.first = static_cast<_Tp*>(::operator new(
                __n * sizeof(_Tp), __al, nothrow));
        } else {
            __r.first = static_cast<_Tp*>(::operator new(
                __n * sizeof(_Tp), nothrow));
        }
#else
    if (__is_overaligned_for_new(_LIBCPP_ALIGNOF(_Tp)))
        {
            // Since aligned operator new is unavailable, return an empty
            // buffer rather than one with invalid alignment.
            return __r;
        }

        __r.first = static_cast<_Tp*>(::operator new(__n * sizeof(_Tp), nothrow));
#endif

        if (__r.first)
        {
            __r.second = __n;
            break;
        }
        __n /= 2;
    }
    return __r;
}

template <class _Tp>
inline _LIBCPP_INLINE_VISIBILITY
void return_temporary_buffer(_Tp* __p) _NOEXCEPT
{
  _VSTD::__libcpp_deallocate_unsized((void*)__p, _LIBCPP_ALIGNOF(_Tp));
}

struct __return_temporary_buffer
{
    template <class _Tp>
    _LIBCPP_INLINE_VISIBILITY void operator()(_Tp* __p) const {_VSTD::return_temporary_buffer(__p);}
};

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___MEMORY_TEMPORARY_BUFFER_H