On Fri, 3 Nov 2023 12:03:24 GMT, Claes Redestad <redes...@openjdk.org> wrote:
> https://github.com/cassioneri/eaf suggest this code for leap year calculation: > > public static boolean isLeap(long year) { > int d = year % 100 != 0 ? 4 : 16; > return (year & (d - 1)) == 0; > } > > .. with a claim this would compile down to branchless, easily pipelined code. > > This doesn't currently happen with C2. In the meantime I think we can improve > the current code in `Year.isLeap` and `IsoChronology.isLeapYear` by > leveraging the fact that the `% 100` check is only needed if `(year & 15) != > 0`: > > > public static boolean isLeap(long year) { > return (year & 15) == 0 ? (year & 3) == 0 : (year & 3) == 0 && year % > 100 != 0; > } > > > Mac M1: > > Name Cnt Base Error Test Error Unit Change > LeapYearBench.isLeapYear 15 0,743 ± 0,009 0,994 ± 0,005 ops/us > 1,34x (p = 0,000*) > LeapYearBench.isLeapYearChrono 15 0,748 ± 0,006 0,991 ± 0,003 ops/us > 1,32x (p = 0,000*) > LeapYearBench.isLeapYearNS 15 0,558 ± 0,026 0,552 ± 0,033 ops/us > 0,99x (p = 0,602 ) > * = significant > > > Linux x64: > > Name Cnt Base Error Test Error Unit Change > LeapYearBench.isLeapYear 15 0.534 ± 0.001 0.765 ± 0.004 ops/us > 1.43x (p = 0.000*) > LeapYearBench.isLeapYearChrono 15 0.535 ± 0.000 0.753 ± 0.040 ops/us > 1.41x (p = 0.000*) > LeapYearBench.isLeapYearNS 15 0.352 ± 0.000 0.351 ± 0.001 ops/us > 1.00x (p = 0.000*) > * = significant > > > 30% higher throughput on M1, 40% on x64. `isLeapYearNS` runs a variant of the > code from https://github.com/cassioneri/eaf ported to java - perhaps the JIT > can be improved to do whatever clang/gcc does here and achieve an even better > speed-up. > > Testing: so far only java/time/tck/java/time locally, will run a few tiers > before filing an enhancement and opening the PR for review. This pull request has now been integrated. Changeset: 7d25f1c6 Author: Claes Redestad <redes...@openjdk.org> URL: https://git.openjdk.org/jdk/commit/7d25f1c6cb770e21cfad8096c1637a24e65fab8c Stats: 125 lines in 6 files changed: 118 ins; 0 del; 7 mod 8319423: Improve Year.isLeap by checking divisibility by 16 Reviewed-by: naoto, rriggs ------------- PR: https://git.openjdk.org/jdk/pull/16491
