libcxx/include/__compare/strong_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_STRONG_ORDER
  10 #define _LIBCPP___COMPARE_STRONG_ORDER
  11
  12 #include <__bit/bit_cast.h>
  13 #include <__compare/compare_three_way.h>
  14 #include <__compare/ordering.h>
  15 #include <__config>
  16 #include <__type_traits/conditional.h>
  17 #include <__type_traits/decay.h>
  18 #include <__utility/forward.h>
  19 #include <__utility/priority_tag.h>
  20 #include <cmath>
  21 #include <cstdint>
  22 #include <limits>
  23
  24 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
  25 #  pragma GCC system_header
  26 #endif
  27
  28 _LIBCPP_PUSH_MACROS
  29 #include <__undef_macros>
  30
  31 _LIBCPP_BEGIN_NAMESPACE_STD
  32
  33 #if _LIBCPP_STD_VER >= 20
  34
  35 // [cmp.alg]
  36 namespace __strong_order {
  37     struct __fn {
  38     // NOLINTBEGIN(libcpp-robust-against-adl) strong_order should use ADL, but only here
  39         template<class _Tp, class _Up>
  40             requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
  41         _LIBCPP_HIDE_FROM_ABI static constexpr auto
  42         __go(_Tp&& __t, _Up&& __u, __priority_tag<2>)
  43             noexcept(noexcept(strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
  44             -> decltype(      strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
  45             { return          strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
  46     // NOLINTEND(libcpp-robust-against-adl)
  47
  48         template<class _Tp, class _Up, class _Dp = decay_t<_Tp>>
  49             requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
  50         _LIBCPP_HIDE_FROM_ABI static constexpr strong_ordering
  51         __go(_Tp&& __t, _Up&& __u, __priority_tag<1>) noexcept
  52         {
  53             if constexpr (numeric_limits<_Dp>::is_iec559 && sizeof(_Dp) == sizeof(int32_t)) {
  54                 int32_t __rx = _VSTD::bit_cast<int32_t>(__t);
  55                 int32_t __ry = _VSTD::bit_cast<int32_t>(__u);
  56                 __rx = (__rx < 0) ? (numeric_limits<int32_t>::min() - __rx - 1) : __rx;
  57                 __ry = (__ry < 0) ? (numeric_limits<int32_t>::min() - __ry - 1) : __ry;
  58                 return (__rx <=> __ry);
  59             } else if constexpr (numeric_limits<_Dp>::is_iec559 && sizeof(_Dp) == sizeof(int64_t)) {
  60                 int64_t __rx = _VSTD::bit_cast<int64_t>(__t);
  61                 int64_t __ry = _VSTD::bit_cast<int64_t>(__u);
  62                 __rx = (__rx < 0) ? (numeric_limits<int64_t>::min() - __rx - 1) : __rx;
  63                 __ry = (__ry < 0) ? (numeric_limits<int64_t>::min() - __ry - 1) : __ry;
  64                 return (__rx <=> __ry);
  65             } else if (__t < __u) {
  66                 return strong_ordering::less;
  67             } else if (__t > __u) {
  68                 return strong_ordering::greater;
  69             } else if (__t == __u) {
  70                 if constexpr (numeric_limits<_Dp>::radix == 2) {
  71                     return _VSTD::signbit(__u) <=> _VSTD::signbit(__t);
  72                 } else {
  73                     // This is bullet 3 of the IEEE754 algorithm, relevant
  74                     // only for decimal floating-point;
  75                     // see https://stackoverflow.com/questions/69068075/
  76                     if (__t == 0 || _VSTD::isinf(__t)) {
  77                         return _VSTD::signbit(__u) <=> _VSTD::signbit(__t);
  78                     } else {
  79                         int __texp, __uexp;
  80                         (void)_VSTD::frexp(__t, &__texp);
  81                         (void)_VSTD::frexp(__u, &__uexp);
  82                         return (__t < 0) ? (__texp <=> __uexp) : (__uexp <=> __texp);
  83                     }
  84                 }
  85             } else {
  86                 // They're unordered, so one of them must be a NAN.
  87                 // The order is -QNAN, -SNAN, numbers, +SNAN, +QNAN.
  88                 bool __t_is_nan = _VSTD::isnan(__t);
  89                 bool __u_is_nan = _VSTD::isnan(__u);
  90                 bool __t_is_negative = _VSTD::signbit(__t);
  91                 bool __u_is_negative = _VSTD::signbit(__u);
  92                 using _IntType = conditional_t<
  93                     sizeof(__t) == sizeof(int32_t), int32_t, conditional_t<
  94                     sizeof(__t) == sizeof(int64_t), int64_t, void>
  95                 >;
  96                 if constexpr (is_same_v<_IntType, void>) {
  97                     static_assert(sizeof(_Dp) == 0, "std::strong_order is unimplemented for this floating-point type");
  98                 } else if (__t_is_nan && __u_is_nan) {
  99                     // Order by sign bit, then by "payload bits" (we'll just use bit_cast).
 100                     if (__t_is_negative != __u_is_negative) {
 101                         return (__u_is_negative <=> __t_is_negative);
 102                     } else {
 103                         return _VSTD::bit_cast<_IntType>(__t) <=> _VSTD::bit_cast<_IntType>(__u);
 104                     }
 105                 } else if (__t_is_nan) {
 106                     return __t_is_negative ? strong_ordering::less : strong_ordering::greater;
 107                 } else {
 108                     return __u_is_negative ? strong_ordering::greater : strong_ordering::less;
 109                 }
 110             }
 111         }
 112
 113         template<class _Tp, class _Up>
 114             requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
 115         _LIBCPP_HIDE_FROM_ABI static constexpr auto
 116         __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
 117             noexcept(noexcept(strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
 118             -> decltype(      strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
 119             { return          strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
 120
 121         template<class _Tp, class _Up>
 122         _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
 123             noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>())))
 124             -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>()))
 125             { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>()); }
 126     };
 127 } // namespace __strong_order
 128
 129 inline namespace __cpo {
 130     inline constexpr auto strong_order = __strong_order::__fn{};
 131 } // namespace __cpo
 132
 133 #endif // _LIBCPP_STD_VER >= 20
 134
 135 _LIBCPP_END_NAMESPACE_STD
 136
 137 _LIBCPP_POP_MACROS
 138
 139 #endif // _LIBCPP___COMPARE_STRONG_ORDER