[libcxx-commits] [libcxx] f537b4e - [libc++] Avoid template instantiations in the duration aliases (#178182)

[via libcxx-commits]

Author: Nikolas Klauser
Date: 2026-02-04T10:26:48+01:00
New Revision: f537b4e51822b19780386e0575ff95e82f8ec445

URL: https://github.com/llvm/llvm-project/commit/f537b4e51822b19780386e0575ff95e82f8ec445
DIFF: https://github.com/llvm/llvm-project/commit/f537b4e51822b19780386e0575ff95e82f8ec445.diff

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

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>`

Added: 
    

Modified: 
    libcxx/include/__chrono/duration.h

Removed: 
    


################################################################################
diff  --git a/libcxx/include/__chrono/duration.h b/libcxx/include/__chrono/duration.h
index 9313fc797ecd5..b7762bd1203ad 100644
--- a/libcxx/include/__chrono/duration.h
+++ b/libcxx/include/__chrono/duration.h
@@ -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 ==