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 <__type_traits/decay.h>
  17 #include <__utility/forward.h>
  18 #include <__utility/priority_tag.h>
  19 #include <cmath>
  20
  21 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
  22 #  pragma GCC system_header
  23 #endif
  24
  25 _LIBCPP_BEGIN_NAMESPACE_STD
  26
  27 #if _LIBCPP_STD_VER >= 20
  28
  29 // [cmp.alg]
  30 namespace __weak_order {
  31     struct __fn {
  32     // NOLINTBEGIN(libcpp-robust-against-adl) weak_order should use ADL, but only here
  33         template<class _Tp, class _Up>
  34             requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  35         _LIBCPP_HIDE_FROM_ABI static constexpr auto
  36         __go(_Tp&& __t, _Up&& __u, __priority_tag<3>)
  37             noexcept(noexcept(weak_ordering(weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
  38             -> decltype(      weak_ordering(weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
  39             { return          weak_ordering(weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
  40     // NOLINTEND(libcpp-robust-against-adl)
  41
  42         template<class _Tp, class _Up, class _Dp = decay_t<_Tp>>
  43             requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
  44         _LIBCPP_HIDE_FROM_ABI static constexpr weak_ordering
  45         __go(_Tp&& __t, _Up&& __u, __priority_tag<2>) noexcept
  46         {
  47             partial_ordering __po = (__t <=> __u);
  48             if (__po == partial_ordering::less) {
  49                 return weak_ordering::less;
  50             } else if (__po == partial_ordering::equivalent) {
  51                 return weak_ordering::equivalent;
  52             } else if (__po == partial_ordering::greater) {
  53                 return weak_ordering::greater;
  54             } else {
  55                 // Otherwise, at least one of them is a NaN.
  56                 bool __t_is_nan = _VSTD::isnan(__t);
  57                 bool __u_is_nan = _VSTD::isnan(__u);
  58                 bool __t_is_negative = _VSTD::signbit(__t);
  59                 bool __u_is_negative = _VSTD::signbit(__u);
  60                 if (__t_is_nan && __u_is_nan) {
  61                     return (__u_is_negative <=> __t_is_negative);
  62                 } else if (__t_is_nan) {
  63                     return __t_is_negative ? weak_ordering::less : weak_ordering::greater;
  64                 } else {
  65                     return __u_is_negative ? weak_ordering::greater : weak_ordering::less;
  66                 }
  67             }
  68         }
  69
  70         template<class _Tp, class _Up>
  71             requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  72         _LIBCPP_HIDE_FROM_ABI static constexpr auto
  73         __go(_Tp&& __t, _Up&& __u, __priority_tag<1>)
  74             noexcept(noexcept(weak_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
  75             -> decltype(      weak_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
  76             { return          weak_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
  77
  78         template<class _Tp, class _Up>
  79             requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  80         _LIBCPP_HIDE_FROM_ABI static constexpr auto
  81         __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
  82             noexcept(noexcept(weak_ordering(_VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
  83             -> decltype(      weak_ordering(_VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
  84             { return          weak_ordering(_VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
  85
  86         template<class _Tp, class _Up>
  87         _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
  88             noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<3>())))
  89             -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<3>()))
  90             { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<3>()); }
  91     };
  92 } // namespace __weak_order
  93
  94 inline namespace __cpo {
  95     inline constexpr auto weak_order = __weak_order::__fn{};
  96 } // namespace __cpo
  97
  98 #endif // _LIBCPP_STD_VER >= 20
  99
 100 _LIBCPP_END_NAMESPACE_STD
 101
 102 #endif // _LIBCPP___COMPARE_WEAK_ORDER