weak_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___COMPARE_WEAK_ORDER
#define _LIBCPP___COMPARE_WEAK_ORDER

#include <__compare/compare_three_way.h>
#include <__compare/ordering.h>
#include <__compare/strong_order.h>
#include <__config>
#include <__math/traits.h>
#include <__type_traits/decay.h>
#include <__type_traits/is_floating_point.h>
#include <__type_traits/is_same.h>
#include <__utility/forward.h>
#include <__utility/priority_tag.h>

#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
#  pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

#if _LIBCPP_STD_VER >= 20

// [cmp.alg]
namespace __weak_order {
void weak_order() = delete;

struct __fn {
  // NOLINTBEGIN(libcpp-robust-against-adl) weak_order should use ADL, but only here
  template <class _Tp, class _Up>
    requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<3>) noexcept(
      noexcept(weak_ordering(weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))))
      -> decltype(weak_ordering(weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) {
    return weak_ordering(weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)));
  }
  // NOLINTEND(libcpp-robust-against-adl)

  template <class _Tp, class _Up, class _Dp = decay_t<_Tp>>
    requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
  _LIBCPP_HIDE_FROM_ABI static constexpr weak_ordering __go(_Tp&& __t, _Up&& __u, __priority_tag<2>) noexcept {
    partial_ordering __po = (__t <=> __u);
    if (__po == partial_ordering::less) {
      return weak_ordering::less;
    } else if (__po == partial_ordering::equivalent) {
      return weak_ordering::equivalent;
    } else if (__po == partial_ordering::greater) {
      return weak_ordering::greater;
    } else {
      // Otherwise, at least one of them is a NaN.
      bool __t_is_nan      = __math::isnan(__t);
      bool __u_is_nan      = __math::isnan(__u);
      bool __t_is_negative = __math::signbit(__t);
      bool __u_is_negative = __math::signbit(__u);
      if (__t_is_nan && __u_is_nan) {
        return (__u_is_negative <=> __t_is_negative);
      } else if (__t_is_nan) {
        return __t_is_negative ? weak_ordering::less : weak_ordering::greater;
      } else {
        return __u_is_negative ? weak_ordering::greater : weak_ordering::less;
      }
    }
  }

  template <class _Tp, class _Up>
    requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<1>) noexcept(
      noexcept(weak_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u)))))
      -> decltype(weak_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) {
    return weak_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u)));
  }

  template <class _Tp, class _Up>
    requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<0>) noexcept(
      noexcept(weak_ordering(std::strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))))
      -> decltype(weak_ordering(std::strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) {
    return weak_ordering(std::strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)));
  }

  template <class _Tp, class _Up>
  _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
      noexcept(noexcept(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<3>())))
          -> decltype(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<3>())) {
    return __go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<3>());
  }
};
} // namespace __weak_order

inline namespace __cpo {
inline constexpr auto weak_order = __weak_order::__fn{};
} // namespace __cpo

#endif // _LIBCPP_STD_VER >= 20

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___COMPARE_WEAK_ORDER