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[libc++] Avoid template instantiations in the duration aliases (#178182)

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These templates are instantiated whenever `<__chrono/duration.h>` is
included, making these calculations quite costly. I also don't think
that folding the calculations decreases readability here (IMO it's
actually easier to read now), so I don't think there is a reason we
shouldn't do this.

`<__chrono/duration.h>` is currently (transitively) included in at least
(I stopped checking) `<algorithm>`, `<atomic>`, `<barrier>`, `<chrono>`,
`<condition_variable>`, `<future>`, `<iomanip>`, `<ios>`, `<iostream>`,
`<istream>`, `<latch>`, `<locale>`, `<mutex>`, `<ostream>`,
`<semaphore>`, `<shared_mutex>`, `<syncstream>` and `<thread>`
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Nikolas Klauser 2026-02-04 10:26:48 +01:00 committed by GitHub
parent 90c632ab48
commit f537b4e518
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1 changed files with 6 additions and 6 deletions
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libcxx/include/__chrono/duration.h
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@ -291,13 +291,13 @@ typedef duration<long long, nano> nanoseconds;
typedef duration<long long, micro> microseconds;
typedef duration<long long, milli> milliseconds;
typedef duration<long long > seconds;
typedef duration< long, ratio< 60> > minutes;
typedef duration< long, ratio<3600> > hours;
typedef duration<long, ratio<60> > minutes;
typedef duration<long, ratio<60 * 60> > hours;
#if _LIBCPP_STD_VER >= 20
typedef duration< int, ratio_multiply<ratio<24>, hours::period>> days;
typedef duration< int, ratio_multiply<ratio<7>, days::period>> weeks;
typedef duration< int, ratio_multiply<ratio<146097, 400>, days::period>> years;
typedef duration< int, ratio_divide<years::period, ratio<12>>> months;
typedef duration<int, ratio<60 * 60 * 24>> days;
typedef duration<int, ratio<60 * 60 * 24 * 7>> weeks;
typedef duration<int, ratio<static_cast<int>(365.2425 * 60 * 60 * 24)>> years;
typedef duration<int, ratio<static_cast<int>(365.2425 * 60 * 60 * 24) / 12>> months;
#endif
// Duration ==