include/__atomic/memory_order.h

//===----------------------------------------------------------------------===//
//
// 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___ATOMIC_MEMORY_ORDER_H
#define _LIBCPP___ATOMIC_MEMORY_ORDER_H

#include <__config>
#include <__type_traits/is_same.h>
#include <__type_traits/underlying_type.h>

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

_LIBCPP_BEGIN_NAMESPACE_STD

// Figure out what the underlying type for `memory_order` would be if it were
// declared as an unscoped enum (accounting for -fshort-enums). Use this result
// to pin the underlying type in C++20.
enum __legacy_memory_order { __mo_relaxed, __mo_consume, __mo_acquire, __mo_release, __mo_acq_rel, __mo_seq_cst };

using __memory_order_underlying_t = underlying_type<__legacy_memory_order>::type;

#if _LIBCPP_STD_VER >= 20

enum class memory_order : __memory_order_underlying_t {
  relaxed = __mo_relaxed,
  consume = __mo_consume,
  acquire = __mo_acquire,
  release = __mo_release,
  acq_rel = __mo_acq_rel,
  seq_cst = __mo_seq_cst
};

static_assert((is_same<underlying_type<memory_order>::type, __memory_order_underlying_t>::value),
              "unexpected underlying type for std::memory_order");

inline constexpr auto memory_order_relaxed = memory_order::relaxed;
inline constexpr auto memory_order_consume = memory_order::consume;
inline constexpr auto memory_order_acquire = memory_order::acquire;
inline constexpr auto memory_order_release = memory_order::release;
inline constexpr auto memory_order_acq_rel = memory_order::acq_rel;
inline constexpr auto memory_order_seq_cst = memory_order::seq_cst;

#else

enum memory_order {
  memory_order_relaxed = __mo_relaxed,
  memory_order_consume = __mo_consume,
  memory_order_acquire = __mo_acquire,
  memory_order_release = __mo_release,
  memory_order_acq_rel = __mo_acq_rel,
  memory_order_seq_cst = __mo_seq_cst,
};

#endif // _LIBCPP_STD_VER >= 20

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___ATOMIC_MEMORY_ORDER_H