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

[Sergey Tsypanov]

On Wed, 15 Mar 2023 11:58:14 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> By avoiding a bit shift operation for the latin1 fast-path test, we can speed up the `java.lang.CharacterData.of` method by ~25% for latin1 code points.
>> 
>> The latin1 test is currently implemented as `ch >>> 8 == 0`.  We can replace this with `ch >= 0 && ch <= 0xFF` for a noticable performance gain (especially for Latin1 code points):
>> 
>> This method is called frequently by various property-determining methods in `java.lang.Character` like `isLowerCase`, `isDigit` etc, so one should expect improvements for all these methods.
>> 
>> Performance is tested using the `Characters.isDigit` benchmark using the digits '0' (decimal 48, in CharacterDataLatin1) and '\u0660' (decimal 1632, in CharacterData00):
>> 
>> Baseline:
>> 
>> 
>> Benchmark           (codePoint)  Mode  Cnt  Score   Error  Units
>> Characters.isDigit           48  avgt   15  0.870 ± 0.011  ns/op
>> Characters.isDigit         1632  avgt   15  2.168 ± 0.017  ns/op
>> 
>> PR:
>> 
>> 
>> Benchmark           (codePoint)  Mode  Cnt  Score   Error  Units
>> Characters.isDigit           48  avgt   15  0.654 ± 0.007  ns/op
>> Characters.isDigit         1632  avgt   15  2.032 ± 0.019  ns/op
>
> src/java.base/share/classes/java/lang/CharacterData.java line 72:
> 
>> 70: 
>> 71:     static final CharacterData of(int ch) {
>> 72:         if (ch >= 0 && ch <= 0xFF) {     // fast-path
> 
> Maybereducing to a single branch with a mask op helps further? Or maybe the JIT already effectively does that:
> 
> `if (ch && 0xFFFFFF00 == 0) {`

Btw, I think we can do the same for `StringLatin1.canEncode()`

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