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1 // -*- C++ -*- operator<=> three-way comparison support.
2 
3 // Copyright (C) 2019-2020 Free Software Foundation, Inc.
4 //
5 // This file is part of GCC.
6 //
7 // GCC is free software; you can redistribute it and/or modify
8 // it under the terms of the GNU General Public License as published by
9 // the Free Software Foundation; either version 3, or (at your option)
10 // any later version.
11 //
12 // GCC is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 // GNU General Public License for more details.
16 //
17 // Under Section 7 of GPL version 3, you are granted additional
18 // permissions described in the GCC Runtime Library Exception, version
19 // 3.1, as published by the Free Software Foundation.
20 
21 // You should have received a copy of the GNU General Public License and
22 // a copy of the GCC Runtime Library Exception along with this program;
23 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
24 // <http://www.gnu.org/licenses/>.
25 
26 /** @file compare
27  * This is a Standard C++ Library header.
28  */
29 
30 #ifndef _COMPARE
31 #define _COMPARE
32 
33 #pragma GCC system_header
34 
35 #if __cplusplus > 201703L && __cpp_impl_three_way_comparison >= 201907L
36 
37 #pragma GCC visibility push(default)
38 
39 #include <concepts>
40 
41 #if __cpp_lib_concepts
42 # define __cpp_lib_three_way_comparison 201711L
43 #endif
44 
45 namespace std
46 {
47  // [cmp.categories], comparison category types
48 
49  namespace __cmp_cat
50  {
51  using type = signed char;
52 
53  enum class _Ord : type { equivalent = 0, less = -1, greater = 1 };
54 
55  enum class _Ncmp : type { _Unordered = 2 };
56 
57  struct __unspec
58  {
59  constexpr __unspec(__unspec*) { }
60  };
61  }
62 
63  class partial_ordering
64  {
65  // less=0xff, equiv=0x00, greater=0x01, unordered=0x02
66  __cmp_cat::type _M_value;
67 
68  constexpr explicit
69  partial_ordering(__cmp_cat::_Ord __v) noexcept
70  : _M_value(__cmp_cat::type(__v))
71  { }
72 
73  constexpr explicit
74  partial_ordering(__cmp_cat::_Ncmp __v) noexcept
75  : _M_value(__cmp_cat::type(__v))
76  { }
77 
78  friend class weak_ordering;
79  friend class strong_ordering;
80 
81  public:
82  // valid values
83  static const partial_ordering less;
84  static const partial_ordering equivalent;
85  static const partial_ordering greater;
86  static const partial_ordering unordered;
87 
88  // comparisons
89  friend constexpr bool
90  operator==(partial_ordering __v, __cmp_cat::__unspec) noexcept
91  { return __v._M_value == 0; }
92 
93  friend constexpr bool
94  operator==(partial_ordering, partial_ordering) noexcept = default;
95 
96  friend constexpr bool
97  operator< (partial_ordering __v, __cmp_cat::__unspec) noexcept
98  { return __v._M_value == -1; }
99 
100  friend constexpr bool
101  operator> (partial_ordering __v, __cmp_cat::__unspec) noexcept
102  { return __v._M_value == 1; }
103 
104  friend constexpr bool
105  operator<=(partial_ordering __v, __cmp_cat::__unspec) noexcept
106  { return __v._M_value <= 0; }
107 
108  friend constexpr bool
109  operator>=(partial_ordering __v, __cmp_cat::__unspec) noexcept
110  { return __cmp_cat::type(__v._M_value & 1) == __v._M_value; }
111 
112  friend constexpr bool
113  operator< (__cmp_cat::__unspec, partial_ordering __v) noexcept
114  { return __v._M_value == 1; }
115 
116  friend constexpr bool
117  operator> (__cmp_cat::__unspec, partial_ordering __v) noexcept
118  { return __v._M_value == -1; }
119 
120  friend constexpr bool
121  operator<=(__cmp_cat::__unspec, partial_ordering __v) noexcept
122  { return __cmp_cat::type(__v._M_value & 1) == __v._M_value; }
123 
124  friend constexpr bool
125  operator>=(__cmp_cat::__unspec, partial_ordering __v) noexcept
126  { return 0 >= __v._M_value; }
127 
128  friend constexpr partial_ordering
129  operator<=>(partial_ordering __v, __cmp_cat::__unspec) noexcept
130  { return __v; }
131 
132  friend constexpr partial_ordering
133  operator<=>(__cmp_cat::__unspec, partial_ordering __v) noexcept
134  {
135  if (__v._M_value & 1)
136  return partial_ordering(__cmp_cat::_Ord(-__v._M_value));
137  else
138  return __v;
139  }
140  };
141 
142  // valid values' definitions
143  inline constexpr partial_ordering
144  partial_ordering::less(__cmp_cat::_Ord::less);
145 
146  inline constexpr partial_ordering
147  partial_ordering::equivalent(__cmp_cat::_Ord::equivalent);
148 
149  inline constexpr partial_ordering
150  partial_ordering::greater(__cmp_cat::_Ord::greater);
151 
152  inline constexpr partial_ordering
153  partial_ordering::unordered(__cmp_cat::_Ncmp::_Unordered);
154 
155  class weak_ordering
156  {
157  __cmp_cat::type _M_value;
158 
159  constexpr explicit
160  weak_ordering(__cmp_cat::_Ord __v) noexcept : _M_value(__cmp_cat::type(__v))
161  { }
162 
163  friend class strong_ordering;
164 
165  public:
166  // valid values
167  static const weak_ordering less;
168  static const weak_ordering equivalent;
169  static const weak_ordering greater;
170 
171  constexpr operator partial_ordering() const noexcept
172  { return partial_ordering(__cmp_cat::_Ord(_M_value)); }
173 
174  // comparisons
175  friend constexpr bool
176  operator==(weak_ordering __v, __cmp_cat::__unspec) noexcept
177  { return __v._M_value == 0; }
178 
179  friend constexpr bool
180  operator==(weak_ordering, weak_ordering) noexcept = default;
181 
182  friend constexpr bool
183  operator< (weak_ordering __v, __cmp_cat::__unspec) noexcept
184  { return __v._M_value < 0; }
185 
186  friend constexpr bool
187  operator> (weak_ordering __v, __cmp_cat::__unspec) noexcept
188  { return __v._M_value > 0; }
189 
190  friend constexpr bool
191  operator<=(weak_ordering __v, __cmp_cat::__unspec) noexcept
192  { return __v._M_value <= 0; }
193 
194  friend constexpr bool
195  operator>=(weak_ordering __v, __cmp_cat::__unspec) noexcept
196  { return __v._M_value >= 0; }
197 
198  friend constexpr bool
199  operator< (__cmp_cat::__unspec, weak_ordering __v) noexcept
200  { return 0 < __v._M_value; }
201 
202  friend constexpr bool
203  operator> (__cmp_cat::__unspec, weak_ordering __v) noexcept
204  { return 0 > __v._M_value; }
205 
206  friend constexpr bool
207  operator<=(__cmp_cat::__unspec, weak_ordering __v) noexcept
208  { return 0 <= __v._M_value; }
209 
210  friend constexpr bool
211  operator>=(__cmp_cat::__unspec, weak_ordering __v) noexcept
212  { return 0 >= __v._M_value; }
213 
214  friend constexpr weak_ordering
215  operator<=>(weak_ordering __v, __cmp_cat::__unspec) noexcept
216  { return __v; }
217 
218  friend constexpr weak_ordering
219  operator<=>(__cmp_cat::__unspec, weak_ordering __v) noexcept
220  { return weak_ordering(__cmp_cat::_Ord(-__v._M_value)); }
221  };
222 
223  // valid values' definitions
224  inline constexpr weak_ordering
225  weak_ordering::less(__cmp_cat::_Ord::less);
226 
227  inline constexpr weak_ordering
228  weak_ordering::equivalent(__cmp_cat::_Ord::equivalent);
229 
230  inline constexpr weak_ordering
231  weak_ordering::greater(__cmp_cat::_Ord::greater);
232 
233  class strong_ordering
234  {
235  __cmp_cat::type _M_value;
236 
237  constexpr explicit
238  strong_ordering(__cmp_cat::_Ord __v) noexcept
239  : _M_value(__cmp_cat::type(__v))
240  { }
241 
242  public:
243  // valid values
244  static const strong_ordering less;
245  static const strong_ordering equal;
246  static const strong_ordering equivalent;
247  static const strong_ordering greater;
248 
249  constexpr operator partial_ordering() const noexcept
250  { return partial_ordering(__cmp_cat::_Ord(_M_value)); }
251 
252  constexpr operator weak_ordering() const noexcept
253  { return weak_ordering(__cmp_cat::_Ord(_M_value)); }
254 
255  // comparisons
256  friend constexpr bool
257  operator==(strong_ordering __v, __cmp_cat::__unspec) noexcept
258  { return __v._M_value == 0; }
259 
260  friend constexpr bool
261  operator==(strong_ordering, strong_ordering) noexcept = default;
262 
263  friend constexpr bool
264  operator< (strong_ordering __v, __cmp_cat::__unspec) noexcept
265  { return __v._M_value < 0; }
266 
267  friend constexpr bool
268  operator> (strong_ordering __v, __cmp_cat::__unspec) noexcept
269  { return __v._M_value > 0; }
270 
271  friend constexpr bool
272  operator<=(strong_ordering __v, __cmp_cat::__unspec) noexcept
273  { return __v._M_value <= 0; }
274 
275  friend constexpr bool
276  operator>=(strong_ordering __v, __cmp_cat::__unspec) noexcept
277  { return __v._M_value >= 0; }
278 
279  friend constexpr bool
280  operator< (__cmp_cat::__unspec, strong_ordering __v) noexcept
281  { return 0 < __v._M_value; }
282 
283  friend constexpr bool
284  operator> (__cmp_cat::__unspec, strong_ordering __v) noexcept
285  { return 0 > __v._M_value; }
286 
287  friend constexpr bool
288  operator<=(__cmp_cat::__unspec, strong_ordering __v) noexcept
289  { return 0 <= __v._M_value; }
290 
291  friend constexpr bool
292  operator>=(__cmp_cat::__unspec, strong_ordering __v) noexcept
293  { return 0 >= __v._M_value; }
294 
295  friend constexpr strong_ordering
296  operator<=>(strong_ordering __v, __cmp_cat::__unspec) noexcept
297  { return __v; }
298 
299  friend constexpr strong_ordering
300  operator<=>(__cmp_cat::__unspec, strong_ordering __v) noexcept
301  { return strong_ordering(__cmp_cat::_Ord(-__v._M_value)); }
302  };
303 
304  // valid values' definitions
305  inline constexpr strong_ordering
306  strong_ordering::less(__cmp_cat::_Ord::less);
307 
308  inline constexpr strong_ordering
309  strong_ordering::equal(__cmp_cat::_Ord::equivalent);
310 
311  inline constexpr strong_ordering
312  strong_ordering::equivalent(__cmp_cat::_Ord::equivalent);
313 
314  inline constexpr strong_ordering
315  strong_ordering::greater(__cmp_cat::_Ord::greater);
316 
317 
318  // named comparison functions
319  constexpr bool
320  is_eq(partial_ordering __cmp) noexcept
321  { return __cmp == 0; }
322 
323  constexpr bool
324  is_neq(partial_ordering __cmp) noexcept
325  { return __cmp != 0; }
326 
327  constexpr bool
328  is_lt (partial_ordering __cmp) noexcept
329  { return __cmp < 0; }
330 
331  constexpr bool
332  is_lteq(partial_ordering __cmp) noexcept
333  { return __cmp <= 0; }
334 
335  constexpr bool
336  is_gt (partial_ordering __cmp) noexcept
337  { return __cmp > 0; }
338 
339  constexpr bool
340  is_gteq(partial_ordering __cmp) noexcept
341  { return __cmp >= 0; }
342 
343  namespace __detail
344  {
345  template<typename _Tp>
346  inline constexpr unsigned __cmp_cat_id = 1;
347  template<>
348  inline constexpr unsigned __cmp_cat_id<partial_ordering> = 2;
349  template<>
350  inline constexpr unsigned __cmp_cat_id<weak_ordering> = 4;
351  template<>
352  inline constexpr unsigned __cmp_cat_id<strong_ordering> = 8;
353 
354  template<typename... _Ts>
355  constexpr auto __common_cmp_cat()
356  {
357  constexpr unsigned __cats = (__cmp_cat_id<_Ts> | ...);
358  // If any Ti is not a comparison category type, U is void.
359  if constexpr (__cats & 1)
360  return;
361  // Otherwise, if at least one Ti is std::partial_ordering,
362  // U is std::partial_ordering.
363  else if constexpr (bool(__cats & __cmp_cat_id<partial_ordering>))
364  return partial_ordering::equivalent;
365  // Otherwise, if at least one Ti is std::weak_ordering,
366  // U is std::weak_ordering.
367  else if constexpr (bool(__cats & __cmp_cat_id<weak_ordering>))
368  return weak_ordering::equivalent;
369  // Otherwise, U is std::strong_ordering.
370  else
371  return strong_ordering::equivalent;
372  }
373  } // namespace __detail
374 
375  // [cmp.common], common comparison category type
376  template<typename... _Ts>
377  struct common_comparison_category
378  {
379  using type = decltype(__detail::__common_cmp_cat<_Ts...>());
380  };
381 
382  // Partial specializations for one and zero argument cases.
383 
384  template<typename _Tp>
385  struct common_comparison_category<_Tp>
386  { using type = void; };
387 
388  template<>
389  struct common_comparison_category<partial_ordering>
390  { using type = partial_ordering; };
391 
392  template<>
393  struct common_comparison_category<weak_ordering>
394  { using type = weak_ordering; };
395 
396  template<>
397  struct common_comparison_category<strong_ordering>
398  { using type = strong_ordering; };
399 
400  template<>
401  struct common_comparison_category<>
402  { using type = strong_ordering; };
403 
404  template<typename... _Ts>
405  using common_comparison_category_t
406  = typename common_comparison_category<_Ts...>::type;
407 
408 #if __cpp_lib_concepts
409  namespace __detail
410  {
411  template<typename _Tp, typename _Cat>
412  concept __compares_as
413  = same_as<common_comparison_category_t<_Tp, _Cat>, _Cat>;
414  } // namespace __detail
415 
416  // [cmp.concept], concept three_way_comparable
417  template<typename _Tp, typename _Cat = partial_ordering>
418  concept three_way_comparable
419  = __detail::__weakly_eq_cmp_with<_Tp, _Tp>
420  && __detail::__partially_ordered_with<_Tp, _Tp>
421  && requires(const remove_reference_t<_Tp>& __a,
422  const remove_reference_t<_Tp>& __b) {
423  { __a <=> __b } -> __detail::__compares_as<_Cat>;
424  };
425 
426  template<typename _Tp, typename _Up, typename _Cat = partial_ordering>
427  concept three_way_comparable_with
428  = three_way_comparable<_Tp, _Cat>
429  && three_way_comparable<_Up, _Cat>
430  && common_reference_with<const remove_reference_t<_Tp>&,
431  const remove_reference_t<_Up>&>
432  && three_way_comparable<
433  common_reference_t<const remove_reference_t<_Tp>&,
434  const remove_reference_t<_Up>&>, _Cat>
435  && __detail::__weakly_eq_cmp_with<_Tp, _Up>
436  && __detail::__partially_ordered_with<_Tp, _Up>
437  && requires(const remove_reference_t<_Tp>& __t,
438  const remove_reference_t<_Up>& __u) {
439  { __t <=> __u } -> __detail::__compares_as<_Cat>;
440  { __u <=> __t } -> __detail::__compares_as<_Cat>;
441  };
442 
443  namespace __detail
444  {
445  template<typename _Tp, typename _Up>
446  using __cmp3way_res_t
447  = decltype(std::declval<_Tp>() <=> std::declval<_Up>());
448 
449  // Implementation of std::compare_three_way_result.
450  // It is undefined for a program to add specializations of
451  // std::compare_three_way_result, so the std::compare_three_way_result_t
452  // alias ignores std::compare_three_way_result and uses
453  // __detail::__cmp3way_res_impl directly instead.
454  template<typename _Tp, typename _Up>
455  struct __cmp3way_res_impl
456  { };
457 
458  template<typename _Tp, typename _Up>
459  requires requires { typename __cmp3way_res_t<__cref<_Tp>, __cref<_Up>>; }
460  struct __cmp3way_res_impl<_Tp, _Up>
461  {
462  using type = __cmp3way_res_t<__cref<_Tp>, __cref<_Up>>;
463  };
464  } // namespace __detail
465 
466  /// [cmp.result], result of three-way comparison
467  template<typename _Tp, typename _Up = _Tp>
468  struct compare_three_way_result
469  : __detail::__cmp3way_res_impl<_Tp, _Up>
470  { };
471 
472  /// [cmp.result], result of three-way comparison
473  template<typename _Tp, typename _Up = _Tp>
474  using compare_three_way_result_t
475  = typename __detail::__cmp3way_res_impl<_Tp, _Up>::type;
476 
477  namespace __detail
478  {
479  // BUILTIN-PTR-THREE-WAY(T, U)
480  template<typename _Tp, typename _Up>
481  concept __3way_builtin_ptr_cmp
482  = three_way_comparable_with<_Tp, _Up>
483  && convertible_to<_Tp, const volatile void*>
484  && convertible_to<_Up, const volatile void*>
485  && ! requires(_Tp&& __t, _Up&& __u)
486  { operator<=>(static_cast<_Tp&&>(__t), static_cast<_Up&&>(__u)); }
487  && ! requires(_Tp&& __t, _Up&& __u)
488  { static_cast<_Tp&&>(__t).operator<=>(static_cast<_Up&&>(__u)); };
489  } // namespace __detail
490 
491  // [cmp.object], typename compare_three_way
492  struct compare_three_way
493  {
494  template<typename _Tp, typename _Up>
495  requires three_way_comparable_with<_Tp, _Up>
496  constexpr auto
497  operator()(_Tp&& __t, _Up&& __u) const noexcept
498  {
499  if constexpr (__detail::__3way_builtin_ptr_cmp<_Tp, _Up>)
500  {
501  auto __pt = static_cast<const volatile void*>(__t);
502  auto __pu = static_cast<const volatile void*>(__u);
503  if (__builtin_is_constant_evaluated())
504  return __pt <=> __pu;
505  auto __it = reinterpret_cast<__UINTPTR_TYPE__>(__pt);
506  auto __iu = reinterpret_cast<__UINTPTR_TYPE__>(__pu);
507  return __it <=> __iu;
508  }
509  else
510  return static_cast<_Tp&&>(__t) <=> static_cast<_Up&&>(__u);
511  }
512 
513  using is_transparent = void;
514  };
515 
516  namespace __cmp_cust
517  {
518  template<floating_point _Tp>
519  constexpr weak_ordering
520  __fp_weak_ordering(_Tp __e, _Tp __f)
521  {
522  // Returns an integer with the same sign as the argument, and magnitude
523  // indicating the classification: zero=1 subnorm=2 norm=3 inf=4 nan=5
524  auto __cat = [](_Tp __fp) -> int {
525  const int __sign = __builtin_signbit(__fp) ? -1 : 1;
526  if (__builtin_isnormal(__fp))
527  return (__fp == 0 ? 1 : 3) * __sign;
528  if (__builtin_isnan(__fp))
529  return 5 * __sign;
530  if (int __inf = __builtin_isinf_sign(__fp))
531  return 4 * __inf;
532  return 2 * __sign;
533  };
534 
535  auto __po = __e <=> __f;
536  if (is_lt(__po))
537  return weak_ordering::less;
538  else if (is_gt(__po))
539  return weak_ordering::greater;
540  else if (__po == partial_ordering::equivalent)
541  return weak_ordering::equivalent;
542  else // unordered, at least one argument is NaN
543  {
544  // return -1 for negative nan, +1 for positive nan, 0 otherwise.
545  auto __isnan_sign = [](_Tp __fp) -> int {
546  return __builtin_isnan(__fp)
547  ? __builtin_signbit(__fp) ? -1 : 1
548  : 0;
549  };
550  auto __ord = __isnan_sign(__e) <=> __isnan_sign(__f);
551  if (is_eq(__ord))
552  return weak_ordering::equivalent;
553  else if (is_lt(__ord))
554  return weak_ordering::less;
555  else
556  return weak_ordering::greater;
557  }
558  }
559 
560  template<typename _Tp, typename _Up>
561  concept __adl_strong = requires(_Tp&& __t, _Up&& __u)
562  {
563  strong_ordering(strong_order(static_cast<_Tp&&>(__t),
564  static_cast<_Up&&>(__u)));
565  };
566 
567  template<typename _Tp, typename _Up>
568  concept __adl_weak = requires(_Tp&& __t, _Up&& __u)
569  {
570  weak_ordering(weak_order(static_cast<_Tp&&>(__t),
571  static_cast<_Up&&>(__u)));
572  };
573 
574  template<typename _Tp, typename _Up>
575  concept __adl_partial = requires(_Tp&& __t, _Up&& __u)
576  {
577  partial_ordering(partial_order(static_cast<_Tp&&>(__t),
578  static_cast<_Up&&>(__u)));
579  };
580 
581  template<typename _Ord, typename _Tp, typename _Up>
582  concept __op_cmp = requires(_Tp&& __t, _Up&& __u)
583  {
584  _Ord(static_cast<_Tp&&>(__t) <=> static_cast<_Up&&>(__u));
585  };
586 
587  template<typename _Tp, typename _Up>
588  concept __strongly_ordered
589  = __adl_strong<_Tp, _Up>
590  // FIXME: || floating_point<remove_reference_t<_Tp>>
591  || __op_cmp<strong_ordering, _Tp, _Up>;
592 
593  class _Strong_order
594  {
595  template<typename _Tp, typename _Up>
596  static constexpr bool
597  _S_noexcept()
598  {
599  if constexpr (floating_point<decay_t<_Tp>>)
600  return true;
601  else if constexpr (__adl_strong<_Tp, _Up>)
602  return noexcept(strong_ordering(strong_order(std::declval<_Tp>(),
603  std::declval<_Up>())));
604  else if constexpr (__op_cmp<strong_ordering, _Tp, _Up>)
605  return noexcept(std::declval<_Tp>() <=> std::declval<_Up>());
606  }
607 
608  friend class _Weak_order;
609  friend class _Strong_fallback;
610 
611  public:
612  template<typename _Tp, typename _Up>
613  requires __strongly_ordered<_Tp, _Up>
614  constexpr strong_ordering
615  operator()(_Tp&& __e, _Up&& __f) const
616  noexcept(_S_noexcept<_Tp, _Up>())
617  {
618  static_assert(same_as<decay_t<_Tp>, decay_t<_Up>>);
619 
620  /* FIXME:
621  if constexpr (floating_point<decay_t<_Tp>>)
622  return __cmp_cust::__fp_strong_order(__e, __f);
623  else */ if constexpr (__adl_strong<_Tp, _Up>)
624  return strong_ordering(strong_order(static_cast<_Tp&&>(__e),
625  static_cast<_Up&&>(__f)));
626  else if constexpr (__op_cmp<strong_ordering, _Tp, _Up>)
627  return static_cast<_Tp&&>(__e) <=> static_cast<_Up&&>(__f);
628  }
629  };
630 
631  template<typename _Tp, typename _Up>
632  concept __weakly_ordered
633  = floating_point<remove_reference_t<_Tp>>
634  || __adl_weak<_Tp, _Up>
635  || __op_cmp<weak_ordering, _Tp, _Up>
636  || __strongly_ordered<_Tp, _Up>;
637 
638  class _Weak_order
639  {
640  template<typename _Tp, typename _Up>
641  static constexpr bool
642  _S_noexcept()
643  {
644  if constexpr (floating_point<decay_t<_Tp>>)
645  return true;
646  else if constexpr (__adl_weak<_Tp, _Up>)
647  return noexcept(weak_ordering(weak_order(std::declval<_Tp>(),
648  std::declval<_Up>())));
649  else if constexpr (__op_cmp<weak_ordering, _Tp, _Up>)
650  return noexcept(std::declval<_Tp>() <=> std::declval<_Up>());
651  else if constexpr (__strongly_ordered<_Tp, _Up>)
652  return _Strong_order::_S_noexcept<_Tp, _Up>();
653  }
654 
655  friend class _Partial_order;
656  friend class _Weak_fallback;
657 
658  public:
659  template<typename _Tp, typename _Up>
660  requires __weakly_ordered<_Tp, _Up>
661  constexpr weak_ordering
662  operator()(_Tp&& __e, _Up&& __f) const
663  noexcept(_S_noexcept<_Tp, _Up>())
664  {
665  static_assert(same_as<decay_t<_Tp>, decay_t<_Up>>);
666 
667  if constexpr (floating_point<decay_t<_Tp>>)
668  return __cmp_cust::__fp_weak_ordering(__e, __f);
669  else if constexpr (__adl_weak<_Tp, _Up>)
670  return weak_ordering(weak_order(static_cast<_Tp&&>(__e),
671  static_cast<_Up&&>(__f)));
672  else if constexpr (__op_cmp<weak_ordering, _Tp, _Up>)
673  return static_cast<_Tp&&>(__e) <=> static_cast<_Up&&>(__f);
674  else if constexpr (__strongly_ordered<_Tp, _Up>)
675  return _Strong_order{}(static_cast<_Tp&&>(__e),
676  static_cast<_Up&&>(__f));
677  }
678  };
679 
680  template<typename _Tp, typename _Up>
681  concept __partially_ordered
682  = __adl_partial<_Tp, _Up>
683  || __op_cmp<partial_ordering, _Tp, _Up>
684  || __weakly_ordered<_Tp, _Up>;
685 
686  class _Partial_order
687  {
688  template<typename _Tp, typename _Up>
689  static constexpr bool
690  _S_noexcept()
691  {
692  if constexpr (__adl_partial<_Tp, _Up>)
693  return noexcept(partial_ordering(partial_order(std::declval<_Tp>(),
694  std::declval<_Up>())));
695  else if constexpr (__op_cmp<partial_ordering, _Tp, _Up>)
696  return noexcept(std::declval<_Tp>() <=> std::declval<_Up>());
697  else if constexpr (__weakly_ordered<_Tp, _Up>)
698  return _Weak_order::_S_noexcept<_Tp, _Up>();
699  }
700 
701  friend class _Partial_fallback;
702 
703  public:
704  template<typename _Tp, typename _Up>
705  requires __partially_ordered<_Tp, _Up>
706  constexpr partial_ordering
707  operator()(_Tp&& __e, _Up&& __f) const
708  noexcept(_S_noexcept<_Tp, _Up>())
709  {
710  static_assert(same_as<decay_t<_Tp>, decay_t<_Up>>);
711 
712  if constexpr (__adl_partial<_Tp, _Up>)
713  return partial_ordering(partial_order(static_cast<_Tp&&>(__e),
714  static_cast<_Up&&>(__f)));
715  else if constexpr (__op_cmp<partial_ordering, _Tp, _Up>)
716  return static_cast<_Tp&&>(__e) <=> static_cast<_Up&&>(__f);
717  else if constexpr (__weakly_ordered<_Tp, _Up>)
718  return _Weak_order{}(static_cast<_Tp&&>(__e),
719  static_cast<_Up&&>(__f));
720  }
721  };
722 
723  template<typename _Tp, typename _Up>
724  concept __op_eq_lt = requires(_Tp&& __t, _Up&& __u)
725  {
726  { static_cast<_Tp&&>(__t) == static_cast<_Up&&>(__u) }
727  -> convertible_to<bool>;
728  { static_cast<_Tp&&>(__t) < static_cast<_Up&&>(__u) }
729  -> convertible_to<bool>;
730  };
731 
732  class _Strong_fallback
733  {
734  template<typename _Tp, typename _Up>
735  static constexpr bool
736  _S_noexcept()
737  {
738  if constexpr (__strongly_ordered<_Tp, _Up>)
739  return _Strong_order::_S_noexcept<_Tp, _Up>();
740  else
741  return noexcept(bool(std::declval<_Tp>() == std::declval<_Up>()))
742  && noexcept(bool(std::declval<_Tp>() < std::declval<_Up>()));
743  }
744 
745  public:
746  template<typename _Tp, typename _Up>
747  requires __strongly_ordered<_Tp, _Up> || __op_eq_lt<_Tp, _Up>
748  constexpr decltype(auto)
749  operator()(_Tp&& __e, _Up&& __f) const
750  noexcept(_S_noexcept<_Tp, _Up>())
751  {
752  static_assert(same_as<decay_t<_Tp>, decay_t<_Up>>);
753 
754  if constexpr (__strongly_ordered<_Tp, _Up>)
755  return _Strong_order{}(static_cast<_Tp&&>(__e),
756  static_cast<_Up&&>(__f));
757  else if constexpr (__op_eq_lt<_Tp, _Up>)
758  return static_cast<_Tp&&>(__e) == static_cast<_Up&&>(__f)
759  ? strong_ordering::equal
760  : static_cast<_Tp&&>(__e) < static_cast<_Up&&>(__f)
761  ? strong_ordering::less
762  : strong_ordering::greater;
763  }
764  };
765 
766  class _Weak_fallback
767  {
768  template<typename _Tp, typename _Up>
769  static constexpr bool
770  _S_noexcept()
771  {
772  if constexpr (__weakly_ordered<_Tp, _Up>)
773  return _Weak_order::_S_noexcept<_Tp, _Up>();
774  else
775  return noexcept(bool(std::declval<_Tp>() == std::declval<_Up>()))
776  && noexcept(bool(std::declval<_Tp>() < std::declval<_Up>()));
777  }
778 
779  public:
780  template<typename _Tp, typename _Up>
781  requires __weakly_ordered<_Tp, _Up> || __op_eq_lt<_Tp, _Up>
782  constexpr decltype(auto)
783  operator()(_Tp&& __e, _Up&& __f) const
784  noexcept(_S_noexcept<_Tp, _Up>())
785  {
786  static_assert(same_as<decay_t<_Tp>, decay_t<_Up>>);
787 
788  if constexpr (__weakly_ordered<_Tp, _Up>)
789  return _Weak_order{}(static_cast<_Tp&&>(__e),
790  static_cast<_Up&&>(__f));
791  else if constexpr (__op_eq_lt<_Tp, _Up>)
792  return static_cast<_Tp&&>(__e) == static_cast<_Up&&>(__f)
793  ? weak_ordering::equivalent
794  : static_cast<_Tp&&>(__e) < static_cast<_Up&&>(__f)
795  ? weak_ordering::less
796  : weak_ordering::greater;
797  }
798  };
799 
800  class _Partial_fallback
801  {
802  template<typename _Tp, typename _Up>
803  static constexpr bool
804  _S_noexcept()
805  {
806  if constexpr (__partially_ordered<_Tp, _Up>)
807  return _Partial_order::_S_noexcept<_Tp, _Up>();
808  else
809  return noexcept(bool(std::declval<_Tp>() == std::declval<_Up>()))
810  && noexcept(bool(std::declval<_Tp>() < std::declval<_Up>()));
811  }
812 
813  public:
814  template<typename _Tp, typename _Up>
815  requires __partially_ordered<_Tp, _Up> || __op_eq_lt<_Tp, _Up>
816  constexpr decltype(auto)
817  operator()(_Tp&& __e, _Up&& __f) const
818  noexcept(_S_noexcept<_Tp, _Up>())
819  {
820  static_assert(same_as<decay_t<_Tp>, decay_t<_Up>>);
821 
822  if constexpr (__partially_ordered<_Tp, _Up>)
823  return _Partial_order{}(static_cast<_Tp&&>(__e),
824  static_cast<_Up&&>(__f));
825  else if constexpr (__op_eq_lt<_Tp, _Up>)
826  return static_cast<_Tp&&>(__e) == static_cast<_Up&&>(__f)
827  ? partial_ordering::equivalent
828  : static_cast<_Tp&&>(__e) < static_cast<_Up&&>(__f)
829  ? partial_ordering::less
830  : static_cast<_Up&&>(__f) < static_cast<_Tp&&>(__e)
831  ? partial_ordering::greater
832  : partial_ordering::unordered;
833  }
834  };
835  } // namespace __cmp_cust
836 
837  // [cmp.alg], comparison algorithms
838  inline namespace __cmp_alg
839  {
840  inline constexpr __cmp_cust::_Strong_order strong_order{};
841 
842  inline constexpr __cmp_cust::_Weak_order weak_order{};
843 
844  inline constexpr __cmp_cust::_Partial_order partial_order{};
845 
846  inline constexpr __cmp_cust::_Strong_fallback
847  compare_strong_order_fallback{};
848 
849  inline constexpr __cmp_cust::_Weak_fallback
850  compare_weak_order_fallback{};
851 
852  inline constexpr __cmp_cust::_Partial_fallback
853  compare_partial_order_fallback{};
854  }
855 
856  namespace __detail
857  {
858  // [expos.only.func]
859  inline constexpr struct _Synth3way
860  {
861  template<typename _Tp, typename _Up>
862  constexpr auto
863  operator()(const _Tp& __t, const _Up& __u) const
864  requires requires
865  {
866  { __t < __u } -> __boolean_testable;
867  { __u < __t } -> __boolean_testable;
868  }
869  {
870  if constexpr (three_way_comparable_with<_Tp, _Up>)
871  return __t <=> __u;
872  else
873  {
874  if (__t < __u)
875  return weak_ordering::less;
876  else if (__u < __t)
877  return weak_ordering::greater;
878  else
879  return weak_ordering::equivalent;
880  }
881  }
882  } __synth3way = {};
883 
884  template<typename _Tp, typename _Up = _Tp>
885  using __synth3way_t
886  = decltype(__detail::__synth3way(std::declval<_Tp&>(),
887  std::declval<_Up&>()));
888  } // namespace __detail
889 #endif // concepts
890 } // namespace std
891 
892 #pragma GCC visibility pop
893 
894 #endif // C++20
895 
896 #endif // _COMPARE