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

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/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.


>From e76983ef81c97fb215d490fa7aeb962807e17820 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Tue, 27 Jan 2026 12:57:52 +0100
Subject: [PATCH] [libc++] Avoid template instantiations in the duration
 aliases

---
 libcxx/include/__chrono/duration.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/libcxx/include/__chrono/duration.h b/libcxx/include/__chrono/duration.h
index 9313fc797ecd5..a9abb5c135e7c 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<31556952>> years;
+typedef duration<int, ratio<31556952 / 12>> months;
 #endif
 // Duration ==