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]
39namespace __strong_order {
40void strong_order() = delete;
41
42struct __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
133inline namespace __cpo {
134inline 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