libcxx/include/__compare/weak_order.h

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef _LIBCPP___COMPARE_WEAK_ORDER
  10 #define _LIBCPP___COMPARE_WEAK_ORDER
  11
  12 #include <__compare/compare_three_way.h>
  13 #include <__compare/ordering.h>
  14 #include <__compare/strong_order.h>
  15 #include <__config>
  16 #include <__math/traits.h>
  17 #include <__type_traits/decay.h>
  18 #include <__type_traits/is_floating_point.h>
  19 #include <__type_traits/is_same.h>
  20 #include <__utility/forward.h>
  21 #include <__utility/priority_tag.h>
  22
  23 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
  24 #  pragma GCC system_header
  25 #endif
  26
  27 _LIBCPP_BEGIN_NAMESPACE_STD
  28
  29 #if _LIBCPP_STD_VER >= 20
  30
  31 // [cmp.alg]
  32 namespace __weak_order {
  33 void weak_order() = delete;
  34
  35 struct __fn {
  36   // NOLINTBEGIN(libcpp-robust-against-adl) weak_order should use ADL, but only here
  37   template <class _Tp, class _Up>
  38     requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  39   _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<3>) noexcept(
  40       noexcept(weak_ordering(weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))))
  41       -> decltype(weak_ordering(weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) {
  42     return weak_ordering(weak_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)));
  43   }
  44   // NOLINTEND(libcpp-robust-against-adl)
  45
  46   template <class _Tp, class _Up, class _Dp = decay_t<_Tp>>
  47     requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
  48   _LIBCPP_HIDE_FROM_ABI static constexpr weak_ordering __go(_Tp&& __t, _Up&& __u, __priority_tag<2>) noexcept {
  49     partial_ordering __po = (__t <=> __u);
  50     if (__po == partial_ordering::less) {
  51       return weak_ordering::less;
  52     } else if (__po == partial_ordering::equivalent) {
  53       return weak_ordering::equivalent;
  54     } else if (__po == partial_ordering::greater) {
  55       return weak_ordering::greater;
  56     } else {
  57       // Otherwise, at least one of them is a NaN.
  58       bool __t_is_nan      = __math::isnan(__t);
  59       bool __u_is_nan      = __math::isnan(__u);
  60       bool __t_is_negative = __math::signbit(__t);
  61       bool __u_is_negative = __math::signbit(__u);
  62       if (__t_is_nan && __u_is_nan) {
  63         return (__u_is_negative <=> __t_is_negative);
  64       } else if (__t_is_nan) {
  65         return __t_is_negative ? weak_ordering::less : weak_ordering::greater;
  66       } else {
  67         return __u_is_negative ? weak_ordering::greater : weak_ordering::less;
  68       }
  69     }
  70   }
  71
  72   template <class _Tp, class _Up>
  73     requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  74   _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<1>) noexcept(
  75       noexcept(weak_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u)))))
  76       -> decltype(weak_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) {
  77     return weak_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u)));
  78   }
  79
  80   template <class _Tp, class _Up>
  81     requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  82   _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<0>) noexcept(
  83       noexcept(weak_ordering(std::strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))))
  84       -> decltype(weak_ordering(std::strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) {
  85     return weak_ordering(std::strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)));
  86   }
  87
  88   template <class _Tp, class _Up>
  89   _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
  90       noexcept(noexcept(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<3>())))
  91           -> decltype(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<3>())) {
  92     return __go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<3>());
  93   }
  94 };
  95 } // namespace __weak_order
  96
  97 inline namespace __cpo {
  98 inline constexpr auto weak_order = __weak_order::__fn{};
  99 } // namespace __cpo
 100
 101 #endif // _LIBCPP_STD_VER >= 20
 102
 103 _LIBCPP_END_NAMESPACE_STD
 104
 105 #endif // _LIBCPP___COMPARE_WEAK_ORDER