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 // UNSUPPORTED: c++03, c++11, c++14, c++17
10 // UNSUPPORTED: libcpp-no-concepts
11 
12 // <compare>
13 
14 // template<class T> constexpr strong_ordering strong_order(const T& a, const T& b);
15 
16 #include <compare>
17 
18 #include <cassert>
19 #include <cmath>
20 #include <iterator> // std::size
21 #include <limits>
22 #include <type_traits>
23 #include <utility>
24 
25 #include "test_macros.h"
26 
27 #if defined(__i386__)
28  #define TEST_BUGGY_SIGNALING_NAN
29 #endif
30 
31 template<class T, class U>
32 constexpr auto has_strong_order(T&& t, U&& u)
33     -> decltype(std::strong_order(static_cast<T&&>(t), static_cast<U&&>(u)), true)
34 {
35     return true;
36 }
37 
38 constexpr bool has_strong_order(...) {
39     return false;
40 }
41 
42 namespace N11 {
43     struct A {};
44     struct B {};
45     std::strong_ordering strong_order(const A&, const A&) { return std::strong_ordering::less; }
46     std::strong_ordering strong_order(const A&, const B&);
47 }
48 
49 void test_1_1()
50 {
51     // If the decayed types of E and F differ, strong_order(E, F) is ill-formed.
52 
53     static_assert( has_strong_order(1, 2));
54     static_assert(!has_strong_order(1, (short)2));
55     static_assert(!has_strong_order(1, 2.0));
56     static_assert(!has_strong_order(1.0f, 2.0));
57 
58     static_assert( has_strong_order((int*)nullptr, (int*)nullptr));
59     static_assert(!has_strong_order((int*)nullptr, (const int*)nullptr));
60     static_assert(!has_strong_order((const int*)nullptr, (int*)nullptr));
61     static_assert( has_strong_order((const int*)nullptr, (const int*)nullptr));
62 
63     N11::A a;
64     N11::B b;
65     static_assert( has_strong_order(a, a));
66     static_assert(!has_strong_order(a, b));
67 }
68 
69 namespace N12 {
70     struct A {};
71     std::strong_ordering strong_order(A&, A&&) { return std::strong_ordering::less; }
72     std::strong_ordering strong_order(A&&, A&&) { return std::strong_ordering::equal; }
73     std::strong_ordering strong_order(const A&, const A&);
74 
75     struct B {
76         friend std::weak_ordering strong_order(B&, B&);
77     };
78 
79     struct StrongOrder {
80         explicit operator std::strong_ordering() const { return std::strong_ordering::less; }
81     };
82     struct C {
83         bool touched = false;
84         friend StrongOrder strong_order(C& lhs, C&) { lhs.touched = true; return StrongOrder(); }
85     };
86 }
87 
88 void test_1_2()
89 {
90     // Otherwise, strong_ordering(strong_order(E, F))
91     // if it is a well-formed expression with overload resolution performed
92     // in a context that does not include a declaration of std::strong_order.
93 
94     // Test that strong_order does not const-qualify the forwarded arguments.
95     N12::A a;
96     assert(std::strong_order(a, std::move(a)) == std::strong_ordering::less);
97     assert(std::strong_order(std::move(a), std::move(a)) == std::strong_ordering::equal);
98 
99     // The type of strong_order(e,f) must be explicitly convertible to strong_ordering.
100     N12::B b;
101     static_assert(!has_strong_order(b, b));
102 
103     N12::C c1, c2;
104     ASSERT_SAME_TYPE(decltype(std::strong_order(c1, c2)), std::strong_ordering);
105     assert(std::strong_order(c1, c2) == std::strong_ordering::less);
106     assert(c1.touched);
107     assert(!c2.touched);
108 }
109 
110 template<class F>
111 constexpr bool test_1_3()
112 {
113     // Otherwise, if the decayed type T of E is a floating-point type,
114     // yields a value of type strong_ordering that is consistent with
115     // the ordering observed by T's comparison operators,
116     // and if numeric_limits<T>::is_iec559 is true, is additionally consistent with
117     // the totalOrder operation as specified in ISO/IEC/IEEE 60559.
118 
119     static_assert(std::numeric_limits<F>::is_iec559);
120 
121     ASSERT_SAME_TYPE(decltype(std::strong_order(F(0), F(0))), std::strong_ordering);
122 
123     F v[] = {
124         -std::numeric_limits<F>::infinity(),
125         std::numeric_limits<F>::lowest(),  // largest (finite) negative number
126         F(-1.0), F(-0.1),
127         -std::numeric_limits<F>::min(),    // smallest (normal) negative number
128         F(-0.0),                           // negative zero
129         F(0.0),
130         std::numeric_limits<F>::min(),     // smallest (normal) positive number
131         F(0.1), F(1.0), F(2.0), F(3.14),
132         std::numeric_limits<F>::max(),     // largest (finite) positive number
133         std::numeric_limits<F>::infinity(),
134     };
135 
136     static_assert(std::size(v) == 14);
137 
138     // Sanity-check that array 'v' is indeed in the right order.
139     for (int i=0; i < 14; ++i) {
140         for (int j=0; j < 14; ++j) {
141             auto naturalOrder = (v[i] <=> v[j]);
142             if (v[i] == 0 && v[j] == 0) {
143                 assert(naturalOrder == std::partial_ordering::equivalent);
144             } else {
145                 assert(naturalOrder == std::partial_ordering::unordered || naturalOrder == (i <=> j));
146             }
147         }
148     }
149 
150     assert(std::strong_order(v[0], v[0]) == std::strong_ordering::equal);
151     assert(std::strong_order(v[0], v[1]) == std::strong_ordering::less);
152     assert(std::strong_order(v[0], v[2]) == std::strong_ordering::less);
153     assert(std::strong_order(v[0], v[3]) == std::strong_ordering::less);
154     assert(std::strong_order(v[0], v[4]) == std::strong_ordering::less);
155     assert(std::strong_order(v[0], v[5]) == std::strong_ordering::less);
156     assert(std::strong_order(v[0], v[6]) == std::strong_ordering::less);
157     assert(std::strong_order(v[0], v[7]) == std::strong_ordering::less);
158     assert(std::strong_order(v[0], v[8]) == std::strong_ordering::less);
159     assert(std::strong_order(v[0], v[9]) == std::strong_ordering::less);
160     assert(std::strong_order(v[0], v[10]) == std::strong_ordering::less);
161     assert(std::strong_order(v[0], v[11]) == std::strong_ordering::less);
162     assert(std::strong_order(v[0], v[12]) == std::strong_ordering::less);
163     assert(std::strong_order(v[0], v[13]) == std::strong_ordering::less);
164     assert(std::strong_order(v[1], v[0]) == std::strong_ordering::greater);
165     assert(std::strong_order(v[1], v[1]) == std::strong_ordering::equal);
166     assert(std::strong_order(v[1], v[2]) == std::strong_ordering::less);
167     assert(std::strong_order(v[1], v[3]) == std::strong_ordering::less);
168     assert(std::strong_order(v[1], v[4]) == std::strong_ordering::less);
169     assert(std::strong_order(v[1], v[5]) == std::strong_ordering::less);
170     assert(std::strong_order(v[1], v[6]) == std::strong_ordering::less);
171     assert(std::strong_order(v[1], v[7]) == std::strong_ordering::less);
172     assert(std::strong_order(v[1], v[8]) == std::strong_ordering::less);
173     assert(std::strong_order(v[1], v[9]) == std::strong_ordering::less);
174     assert(std::strong_order(v[1], v[10]) == std::strong_ordering::less);
175     assert(std::strong_order(v[1], v[11]) == std::strong_ordering::less);
176     assert(std::strong_order(v[1], v[12]) == std::strong_ordering::less);
177     assert(std::strong_order(v[1], v[13]) == std::strong_ordering::less);
178     assert(std::strong_order(v[2], v[0]) == std::strong_ordering::greater);
179     assert(std::strong_order(v[2], v[1]) == std::strong_ordering::greater);
180     assert(std::strong_order(v[2], v[2]) == std::strong_ordering::equal);
181     assert(std::strong_order(v[2], v[3]) == std::strong_ordering::less);
182     assert(std::strong_order(v[2], v[4]) == std::strong_ordering::less);
183     assert(std::strong_order(v[2], v[5]) == std::strong_ordering::less);
184     assert(std::strong_order(v[2], v[6]) == std::strong_ordering::less);
185     assert(std::strong_order(v[2], v[7]) == std::strong_ordering::less);
186     assert(std::strong_order(v[2], v[8]) == std::strong_ordering::less);
187     assert(std::strong_order(v[2], v[9]) == std::strong_ordering::less);
188     assert(std::strong_order(v[2], v[10]) == std::strong_ordering::less);
189     assert(std::strong_order(v[2], v[11]) == std::strong_ordering::less);
190     assert(std::strong_order(v[2], v[12]) == std::strong_ordering::less);
191     assert(std::strong_order(v[2], v[13]) == std::strong_ordering::less);
192     assert(std::strong_order(v[3], v[0]) == std::strong_ordering::greater);
193     assert(std::strong_order(v[3], v[1]) == std::strong_ordering::greater);
194     assert(std::strong_order(v[3], v[2]) == std::strong_ordering::greater);
195     assert(std::strong_order(v[3], v[3]) == std::strong_ordering::equal);
196     assert(std::strong_order(v[3], v[4]) == std::strong_ordering::less);
197     assert(std::strong_order(v[3], v[5]) == std::strong_ordering::less);
198     assert(std::strong_order(v[3], v[6]) == std::strong_ordering::less);
199     assert(std::strong_order(v[3], v[7]) == std::strong_ordering::less);
200     assert(std::strong_order(v[3], v[8]) == std::strong_ordering::less);
201     assert(std::strong_order(v[3], v[9]) == std::strong_ordering::less);
202     assert(std::strong_order(v[3], v[10]) == std::strong_ordering::less);
203     assert(std::strong_order(v[3], v[11]) == std::strong_ordering::less);
204     assert(std::strong_order(v[3], v[12]) == std::strong_ordering::less);
205     assert(std::strong_order(v[3], v[13]) == std::strong_ordering::less);
206     assert(std::strong_order(v[4], v[0]) == std::strong_ordering::greater);
207     assert(std::strong_order(v[4], v[1]) == std::strong_ordering::greater);
208     assert(std::strong_order(v[4], v[2]) == std::strong_ordering::greater);
209     assert(std::strong_order(v[4], v[3]) == std::strong_ordering::greater);
210     assert(std::strong_order(v[4], v[4]) == std::strong_ordering::equal);
211     assert(std::strong_order(v[4], v[5]) == std::strong_ordering::less);
212     assert(std::strong_order(v[4], v[6]) == std::strong_ordering::less);
213     assert(std::strong_order(v[4], v[7]) == std::strong_ordering::less);
214     assert(std::strong_order(v[4], v[8]) == std::strong_ordering::less);
215     assert(std::strong_order(v[4], v[9]) == std::strong_ordering::less);
216     assert(std::strong_order(v[4], v[10]) == std::strong_ordering::less);
217     assert(std::strong_order(v[4], v[11]) == std::strong_ordering::less);
218     assert(std::strong_order(v[4], v[12]) == std::strong_ordering::less);
219     assert(std::strong_order(v[4], v[13]) == std::strong_ordering::less);
220     assert(std::strong_order(v[5], v[0]) == std::strong_ordering::greater);
221     assert(std::strong_order(v[5], v[1]) == std::strong_ordering::greater);
222     assert(std::strong_order(v[5], v[2]) == std::strong_ordering::greater);
223     assert(std::strong_order(v[5], v[3]) == std::strong_ordering::greater);
224     assert(std::strong_order(v[5], v[4]) == std::strong_ordering::greater);
225     assert(std::strong_order(v[5], v[5]) == std::strong_ordering::equal);
226     assert(std::strong_order(v[5], v[6]) == std::strong_ordering::less);
227     assert(std::strong_order(v[5], v[7]) == std::strong_ordering::less);
228     assert(std::strong_order(v[5], v[8]) == std::strong_ordering::less);
229     assert(std::strong_order(v[5], v[9]) == std::strong_ordering::less);
230     assert(std::strong_order(v[5], v[10]) == std::strong_ordering::less);
231     assert(std::strong_order(v[5], v[11]) == std::strong_ordering::less);
232     assert(std::strong_order(v[5], v[12]) == std::strong_ordering::less);
233     assert(std::strong_order(v[5], v[13]) == std::strong_ordering::less);
234     assert(std::strong_order(v[6], v[0]) == std::strong_ordering::greater);
235     assert(std::strong_order(v[6], v[1]) == std::strong_ordering::greater);
236     assert(std::strong_order(v[6], v[2]) == std::strong_ordering::greater);
237     assert(std::strong_order(v[6], v[3]) == std::strong_ordering::greater);
238     assert(std::strong_order(v[6], v[4]) == std::strong_ordering::greater);
239     assert(std::strong_order(v[6], v[5]) == std::strong_ordering::greater);
240     assert(std::strong_order(v[6], v[6]) == std::strong_ordering::equal);
241     assert(std::strong_order(v[6], v[7]) == std::strong_ordering::less);
242     assert(std::strong_order(v[6], v[8]) == std::strong_ordering::less);
243     assert(std::strong_order(v[6], v[9]) == std::strong_ordering::less);
244     assert(std::strong_order(v[6], v[10]) == std::strong_ordering::less);
245     assert(std::strong_order(v[6], v[11]) == std::strong_ordering::less);
246     assert(std::strong_order(v[6], v[12]) == std::strong_ordering::less);
247     assert(std::strong_order(v[6], v[13]) == std::strong_ordering::less);
248     assert(std::strong_order(v[7], v[0]) == std::strong_ordering::greater);
249     assert(std::strong_order(v[7], v[1]) == std::strong_ordering::greater);
250     assert(std::strong_order(v[7], v[2]) == std::strong_ordering::greater);
251     assert(std::strong_order(v[7], v[3]) == std::strong_ordering::greater);
252     assert(std::strong_order(v[7], v[4]) == std::strong_ordering::greater);
253     assert(std::strong_order(v[7], v[5]) == std::strong_ordering::greater);
254     assert(std::strong_order(v[7], v[6]) == std::strong_ordering::greater);
255     assert(std::strong_order(v[7], v[7]) == std::strong_ordering::equal);
256     assert(std::strong_order(v[7], v[8]) == std::strong_ordering::less);
257     assert(std::strong_order(v[7], v[9]) == std::strong_ordering::less);
258     assert(std::strong_order(v[7], v[10]) == std::strong_ordering::less);
259     assert(std::strong_order(v[7], v[11]) == std::strong_ordering::less);
260     assert(std::strong_order(v[7], v[12]) == std::strong_ordering::less);
261     assert(std::strong_order(v[7], v[13]) == std::strong_ordering::less);
262     assert(std::strong_order(v[8], v[0]) == std::strong_ordering::greater);
263     assert(std::strong_order(v[8], v[1]) == std::strong_ordering::greater);
264     assert(std::strong_order(v[8], v[2]) == std::strong_ordering::greater);
265     assert(std::strong_order(v[8], v[3]) == std::strong_ordering::greater);
266     assert(std::strong_order(v[8], v[4]) == std::strong_ordering::greater);
267     assert(std::strong_order(v[8], v[5]) == std::strong_ordering::greater);
268     assert(std::strong_order(v[8], v[6]) == std::strong_ordering::greater);
269     assert(std::strong_order(v[8], v[7]) == std::strong_ordering::greater);
270     assert(std::strong_order(v[8], v[8]) == std::strong_ordering::equal);
271     assert(std::strong_order(v[8], v[9]) == std::strong_ordering::less);
272     assert(std::strong_order(v[8], v[10]) == std::strong_ordering::less);
273     assert(std::strong_order(v[8], v[11]) == std::strong_ordering::less);
274     assert(std::strong_order(v[8], v[12]) == std::strong_ordering::less);
275     assert(std::strong_order(v[8], v[13]) == std::strong_ordering::less);
276     assert(std::strong_order(v[9], v[0]) == std::strong_ordering::greater);
277     assert(std::strong_order(v[9], v[1]) == std::strong_ordering::greater);
278     assert(std::strong_order(v[9], v[2]) == std::strong_ordering::greater);
279     assert(std::strong_order(v[9], v[3]) == std::strong_ordering::greater);
280     assert(std::strong_order(v[9], v[4]) == std::strong_ordering::greater);
281     assert(std::strong_order(v[9], v[5]) == std::strong_ordering::greater);
282     assert(std::strong_order(v[9], v[6]) == std::strong_ordering::greater);
283     assert(std::strong_order(v[9], v[7]) == std::strong_ordering::greater);
284     assert(std::strong_order(v[9], v[8]) == std::strong_ordering::greater);
285     assert(std::strong_order(v[9], v[9]) == std::strong_ordering::equal);
286     assert(std::strong_order(v[9], v[10]) == std::strong_ordering::less);
287     assert(std::strong_order(v[9], v[11]) == std::strong_ordering::less);
288     assert(std::strong_order(v[9], v[12]) == std::strong_ordering::less);
289     assert(std::strong_order(v[9], v[13]) == std::strong_ordering::less);
290     assert(std::strong_order(v[10], v[0]) == std::strong_ordering::greater);
291     assert(std::strong_order(v[10], v[1]) == std::strong_ordering::greater);
292     assert(std::strong_order(v[10], v[2]) == std::strong_ordering::greater);
293     assert(std::strong_order(v[10], v[3]) == std::strong_ordering::greater);
294     assert(std::strong_order(v[10], v[4]) == std::strong_ordering::greater);
295     assert(std::strong_order(v[10], v[5]) == std::strong_ordering::greater);
296     assert(std::strong_order(v[10], v[6]) == std::strong_ordering::greater);
297     assert(std::strong_order(v[10], v[7]) == std::strong_ordering::greater);
298     assert(std::strong_order(v[10], v[8]) == std::strong_ordering::greater);
299     assert(std::strong_order(v[10], v[9]) == std::strong_ordering::greater);
300     assert(std::strong_order(v[10], v[10]) == std::strong_ordering::equal);
301     assert(std::strong_order(v[10], v[11]) == std::strong_ordering::less);
302     assert(std::strong_order(v[10], v[12]) == std::strong_ordering::less);
303     assert(std::strong_order(v[10], v[13]) == std::strong_ordering::less);
304     assert(std::strong_order(v[11], v[0]) == std::strong_ordering::greater);
305     assert(std::strong_order(v[11], v[1]) == std::strong_ordering::greater);
306     assert(std::strong_order(v[11], v[2]) == std::strong_ordering::greater);
307     assert(std::strong_order(v[11], v[3]) == std::strong_ordering::greater);
308     assert(std::strong_order(v[11], v[4]) == std::strong_ordering::greater);
309     assert(std::strong_order(v[11], v[5]) == std::strong_ordering::greater);
310     assert(std::strong_order(v[11], v[6]) == std::strong_ordering::greater);
311     assert(std::strong_order(v[11], v[7]) == std::strong_ordering::greater);
312     assert(std::strong_order(v[11], v[8]) == std::strong_ordering::greater);
313     assert(std::strong_order(v[11], v[9]) == std::strong_ordering::greater);
314     assert(std::strong_order(v[11], v[10]) == std::strong_ordering::greater);
315     assert(std::strong_order(v[11], v[11]) == std::strong_ordering::equal);
316     assert(std::strong_order(v[11], v[12]) == std::strong_ordering::less);
317     assert(std::strong_order(v[11], v[13]) == std::strong_ordering::less);
318     assert(std::strong_order(v[12], v[0]) == std::strong_ordering::greater);
319     assert(std::strong_order(v[12], v[1]) == std::strong_ordering::greater);
320     assert(std::strong_order(v[12], v[2]) == std::strong_ordering::greater);
321     assert(std::strong_order(v[12], v[3]) == std::strong_ordering::greater);
322     assert(std::strong_order(v[12], v[4]) == std::strong_ordering::greater);
323     assert(std::strong_order(v[12], v[5]) == std::strong_ordering::greater);
324     assert(std::strong_order(v[12], v[6]) == std::strong_ordering::greater);
325     assert(std::strong_order(v[12], v[7]) == std::strong_ordering::greater);
326     assert(std::strong_order(v[12], v[8]) == std::strong_ordering::greater);
327     assert(std::strong_order(v[12], v[9]) == std::strong_ordering::greater);
328     assert(std::strong_order(v[12], v[10]) == std::strong_ordering::greater);
329     assert(std::strong_order(v[12], v[11]) == std::strong_ordering::greater);
330     assert(std::strong_order(v[12], v[12]) == std::strong_ordering::equal);
331     assert(std::strong_order(v[12], v[13]) == std::strong_ordering::less);
332     assert(std::strong_order(v[13], v[0]) == std::strong_ordering::greater);
333     assert(std::strong_order(v[13], v[1]) == std::strong_ordering::greater);
334     assert(std::strong_order(v[13], v[2]) == std::strong_ordering::greater);
335     assert(std::strong_order(v[13], v[3]) == std::strong_ordering::greater);
336     assert(std::strong_order(v[13], v[4]) == std::strong_ordering::greater);
337     assert(std::strong_order(v[13], v[5]) == std::strong_ordering::greater);
338     assert(std::strong_order(v[13], v[6]) == std::strong_ordering::greater);
339     assert(std::strong_order(v[13], v[7]) == std::strong_ordering::greater);
340     assert(std::strong_order(v[13], v[8]) == std::strong_ordering::greater);
341     assert(std::strong_order(v[13], v[9]) == std::strong_ordering::greater);
342     assert(std::strong_order(v[13], v[10]) == std::strong_ordering::greater);
343     assert(std::strong_order(v[13], v[11]) == std::strong_ordering::greater);
344     assert(std::strong_order(v[13], v[12]) == std::strong_ordering::greater);
345     assert(std::strong_order(v[13], v[13]) == std::strong_ordering::equal);
346 
347 
348     // There's no way to produce a specifically positive or negative NAN
349     // at compile-time, so the NAN-related tests must be runtime-only.
350     // Also, x86-32 (x87 floating point) cannot handle signaling NANs;
351     // see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=57484 for context.
352 
353     if (!std::is_constant_evaluated()) {
354         F nq = _VSTD::copysign(std::numeric_limits<F>::quiet_NaN(), F(-1));
355         F ns = _VSTD::copysign(std::numeric_limits<F>::signaling_NaN(), F(-1));
356         F ps = _VSTD::copysign(std::numeric_limits<F>::signaling_NaN(), F(+1));
357         F pq = _VSTD::copysign(std::numeric_limits<F>::quiet_NaN(), F(+1));
358 
359         assert(std::strong_order(nq, nq) == std::strong_ordering::equal);
360 #ifndef TEST_BUGGY_SIGNALING_NAN
361         assert(std::strong_order(nq, ns) == std::strong_ordering::less);
362 #endif
363         for (int i=0; i < 14; ++i) {
364             assert(std::strong_order(nq, v[i]) == std::strong_ordering::less);
365         }
366         assert(std::strong_order(nq, ps) == std::strong_ordering::less);
367         assert(std::strong_order(nq, pq) == std::strong_ordering::less);
368 
369 #ifndef TEST_BUGGY_SIGNALING_NAN
370         assert(std::strong_order(ns, nq) == std::strong_ordering::greater);
371 #endif
372         assert(std::strong_order(ns, ns) == std::strong_ordering::equal);
373         for (int i=0; i < 14; ++i) {
374             assert(std::strong_order(ns, v[i]) == std::strong_ordering::less);
375         }
376         assert(std::strong_order(ns, ps) == std::strong_ordering::less);
377         assert(std::strong_order(ns, pq) == std::strong_ordering::less);
378 
379         assert(std::strong_order(ps, nq) == std::strong_ordering::greater);
380         assert(std::strong_order(ps, ns) == std::strong_ordering::greater);
381         for (int i=0; i < 14; ++i) {
382             assert(std::strong_order(ps, v[i]) == std::strong_ordering::greater);
383         }
384         assert(std::strong_order(ps, ps) == std::strong_ordering::equal);
385 #ifndef TEST_BUGGY_SIGNALING_NAN
386         assert(std::strong_order(ps, pq) == std::strong_ordering::less);
387 #endif
388 
389         assert(std::strong_order(pq, nq) == std::strong_ordering::greater);
390         assert(std::strong_order(pq, ns) == std::strong_ordering::greater);
391         for (int i=0; i < 14; ++i) {
392             assert(std::strong_order(pq, v[i]) == std::strong_ordering::greater);
393         }
394 #ifndef TEST_BUGGY_SIGNALING_NAN
395         assert(std::strong_order(pq, ps) == std::strong_ordering::greater);
396 #endif
397         assert(std::strong_order(pq, pq) == std::strong_ordering::equal);
398     }
399 
400     return true;
401 }
402 
403 namespace N14 {
404     // Compare to N12::A.
405     struct A {};
406     bool operator==(const A&, const A&);
407     constexpr std::strong_ordering operator<=>(A&, A&&) { return std::strong_ordering::less; }
408     constexpr std::strong_ordering operator<=>(A&&, A&&) { return std::strong_ordering::equal; }
409     std::strong_ordering operator<=>(const A&, const A&);
410     static_assert(std::three_way_comparable<A>);
411 
412     struct B {
413         std::strong_ordering operator<=>(const B&) const;  // lacks operator==
414     };
415     static_assert(!std::three_way_comparable<B>);
416 
417     struct C {
418         bool *touched;
419         bool operator==(const C&) const;
420         constexpr std::strong_ordering operator<=>(const C& rhs) const {
421             *rhs.touched = true;
422             return std::strong_ordering::equal;
423         }
424     };
425     static_assert(std::three_way_comparable<C>);
426 }
427 
428 constexpr bool test_1_4()
429 {
430     // Otherwise, strong_ordering(compare_three_way()(E, F)) if it is a well-formed expression.
431 
432     // Test neither strong_order nor compare_three_way const-qualify the forwarded arguments.
433     N14::A a;
434     assert(std::strong_order(a, std::move(a)) == std::strong_ordering::less);
435     assert(std::strong_order(std::move(a), std::move(a)) == std::strong_ordering::equal);
436 
437     N14::B b;
438     static_assert(!has_strong_order(b, b));
439 
440     // Test that the arguments are passed to <=> in the correct order.
441     bool c1_touched = false;
442     bool c2_touched = false;
443     N14::C c1 = {&c1_touched};
444     N14::C c2 = {&c2_touched};
445     assert(std::strong_order(c1, c2) == std::strong_ordering::equal);
446     assert(!c1_touched);
447     assert(c2_touched);
448 
449     return true;
450 }
451 
452 int main(int, char**)
453 {
454     test_1_1();
455     test_1_2();
456     test_1_3<float>();
457     test_1_3<double>();
458     // test_1_3<long double>();  // UNIMPLEMENTED
459     test_1_4();
460 
461     static_assert(test_1_3<float>());
462     static_assert(test_1_3<double>());
463     // static_assert(test_1_3<long double>());  // UNIMPLEMENTED
464     static_assert(test_1_4());
465 
466     return 0;
467 }
468