<i18n dev> RFR: 8304245: Speed up CharacterData.of by avoiding bit shifting in the latin1 fast-path test

[Eirik Bjorsnos]

On Wed, 15 Mar 2023 12:15:39 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> It seems reasonable to keep these two in sync, yes. (`CharacterData.of` could even call into `StringLatin1.canEncode`, unless that's cause for some performance anomaly)
>
>> `if (ch && 0xFFFFFF00 == 0) {`
> 
> This seems to perform similar to baseline:
> 
> 
> Benchmark           (codePoint)  Mode  Cnt  Score   Error  Units
> Characters.isDigit           48  avgt   15  0.890 ± 0.025  ns/op
> Characters.isDigit         1632  avgt   15  2.174 ± 0.011  ns/op
> 
> 
> Would be interesting to check the performance on non-Intel architectures. If you want to give it a spin on your M1, here's the benchmark command I used:
> 
> `make test TEST='micro:java.lang.Characters.isDigit' MICRO="OPTIONS=-p codePoint=48,1632"`

> It seems reasonable to keep these two in sync, yes. (`CharacterData.of` could even call into `StringLatin1.canEncode`, unless that's cause for some performance anomaly)

If I update `StringLatin1.canEncode` and call into that from `CharacterData.of`, I observe no regression for the Latin1 case, but a significant regression for the non-Latin1 case. I have no idea how to explain that:


Benchmark           (codePoint)  Mode  Cnt  Score   Error  Units
Characters.isDigit           48  avgt   15  0.675 ± 0.029  ns/op
Characters.isDigit         1632  avgt   15  2.435 ± 0.032  ns/op

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PR: https://git.openjdk.org/jdk/pull/13040