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 <__math/exponential_functions.h> 17 #include <__math/traits.h> 18 #include <__type_traits/conditional.h> 19 #include <__type_traits/decay.h> 20 #include <__type_traits/is_floating_point.h> 21 #include <__type_traits/is_same.h> 22 #include <__utility/forward.h> 23 #include <__utility/priority_tag.h> 24 #include <cstdint> 25 #include <limits> 26 27 #ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER 28 # pragma GCC system_header 29 #endif 30 31 _LIBCPP_PUSH_MACROS 32 #include <__undef_macros> 33 34 _LIBCPP_BEGIN_NAMESPACE_STD 35 36 #if _LIBCPP_STD_VER >= 20 37 38 // [cmp.alg] 39 namespace __strong_order { 40 void strong_order() = delete; 41 42 struct __fn { 43 // NOLINTBEGIN(libcpp-robust-against-adl) strong_order should use ADL, but only here 44 template <class _Tp, class _Up> 45 requires is_same_v<decay_t<_Tp>, decay_t<_Up>> 46 _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<2>) noexcept( 47 noexcept(strong_ordering(strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))))) 48 -> decltype(strong_ordering(strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) { 49 return strong_ordering(strong_order(std::forward<_Tp>(__t), std::forward<_Up>(__u))); 50 } 51 // NOLINTEND(libcpp-robust-against-adl) 52 53 template <class _Tp, class _Up, class _Dp = decay_t<_Tp>> 54 requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp> 55 _LIBCPP_HIDE_FROM_ABI static constexpr strong_ordering __go(_Tp&& __t, _Up&& __u, __priority_tag<1>) noexcept { 56 if constexpr (numeric_limits<_Dp>::is_iec559 && sizeof(_Dp) == sizeof(int32_t)) { 57 int32_t __rx = std::bit_cast<int32_t>(__t); 58 int32_t __ry = std::bit_cast<int32_t>(__u); 59 __rx = (__rx < 0) ? (numeric_limits<int32_t>::min() - __rx - 1) : __rx; 60 __ry = (__ry < 0) ? (numeric_limits<int32_t>::min() - __ry - 1) : __ry; 61 return (__rx <=> __ry); 62 } else if constexpr (numeric_limits<_Dp>::is_iec559 && sizeof(_Dp) == sizeof(int64_t)) { 63 int64_t __rx = std::bit_cast<int64_t>(__t); 64 int64_t __ry = std::bit_cast<int64_t>(__u); 65 __rx = (__rx < 0) ? (numeric_limits<int64_t>::min() - __rx - 1) : __rx; 66 __ry = (__ry < 0) ? (numeric_limits<int64_t>::min() - __ry - 1) : __ry; 67 return (__rx <=> __ry); 68 } else if (__t < __u) { 69 return strong_ordering::less; 70 } else if (__t > __u) { 71 return strong_ordering::greater; 72 } else if (__t == __u) { 73 if constexpr (numeric_limits<_Dp>::radix == 2) { 74 return __math::signbit(__u) <=> __math::signbit(__t); 75 } else { 76 // This is bullet 3 of the IEEE754 algorithm, relevant 77 // only for decimal floating-point; 78 // see https://stackoverflow.com/questions/69068075/ 79 if (__t == 0 || __math::isinf(__t)) { 80 return __math::signbit(__u) <=> __math::signbit(__t); 81 } else { 82 int __texp, __uexp; 83 (void)__math::frexp(__t, &__texp); 84 (void)__math::frexp(__u, &__uexp); 85 return (__t < 0) ? (__texp <=> __uexp) : (__uexp <=> __texp); 86 } 87 } 88 } else { 89 // They're unordered, so one of them must be a NAN. 90 // The order is -QNAN, -SNAN, numbers, +SNAN, +QNAN. 91 bool __t_is_nan = __math::isnan(__t); 92 bool __u_is_nan = __math::isnan(__u); 93 bool __t_is_negative = __math::signbit(__t); 94 bool __u_is_negative = __math::signbit(__u); 95 using _IntType = 96 conditional_t< sizeof(__t) == sizeof(int32_t), 97 int32_t, 98 conditional_t< sizeof(__t) == sizeof(int64_t), int64_t, void> >; 99 if constexpr (is_same_v<_IntType, void>) { 100 static_assert(sizeof(_Dp) == 0, "std::strong_order is unimplemented for this floating-point type"); 101 } else if (__t_is_nan && __u_is_nan) { 102 // Order by sign bit, then by "payload bits" (we'll just use bit_cast). 103 if (__t_is_negative != __u_is_negative) { 104 return (__u_is_negative <=> __t_is_negative); 105 } else { 106 return std::bit_cast<_IntType>(__t) <=> std::bit_cast<_IntType>(__u); 107 } 108 } else if (__t_is_nan) { 109 return __t_is_negative ? strong_ordering::less : strong_ordering::greater; 110 } else { 111 return __u_is_negative ? strong_ordering::greater : strong_ordering::less; 112 } 113 } 114 } 115 116 template <class _Tp, class _Up> 117 requires is_same_v<decay_t<_Tp>, decay_t<_Up>> 118 _LIBCPP_HIDE_FROM_ABI static constexpr auto __go(_Tp&& __t, _Up&& __u, __priority_tag<0>) noexcept( 119 noexcept(strong_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u))))) 120 -> decltype(strong_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u)))) { 121 return strong_ordering(compare_three_way()(std::forward<_Tp>(__t), std::forward<_Up>(__u))); 122 } 123 124 template <class _Tp, class _Up> 125 _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const 126 noexcept(noexcept(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<2>()))) 127 -> decltype(__go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<2>())) { 128 return __go(std::forward<_Tp>(__t), std::forward<_Up>(__u), __priority_tag<2>()); 129 } 130 }; 131 } // namespace __strong_order 132 133 inline namespace __cpo { 134 inline constexpr auto strong_order = __strong_order::__fn{}; 135 } // namespace __cpo 136 137 #endif // _LIBCPP_STD_VER >= 20 138 139 _LIBCPP_END_NAMESPACE_STD 140 141 _LIBCPP_POP_MACROS 142 143 #endif // _LIBCPP___COMPARE_STRONG_ORDER 144