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.
-------------
Commit messages:
- Add comment
- Delegate IsoChronology.isLeapYear to Year.isLeap (both specified to behave
identically), add microbenchmark testing the variant that optimize well with gcc
- Merge branch 'master' into leapyear
- Leap year optimization inspired by Neri & Schneider
Changes: https://git.openjdk.org/jdk/pull/16491/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16491&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8319423
Stats: 101 lines in 3 files changed: 99 ins; 0 del; 2 mod
Patch: https://git.openjdk.org/jdk/pull/16491.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/16491/head:pull/16491
PR: https://git.openjdk.org/jdk/pull/16491
