<i18n dev> RFR: 8302871: Speed up StringLatin1.regionMatchesCI

[David Schlosnagle]

On Sat, 18 Feb 2023 19:45:34 GMT, Eirik Bjorsnos <duke at openjdk.org> wrote:

>> src/java.base/share/classes/java/lang/CharacterDataLatin1.java.template line 181:
>> 
>>> 179:          return ( U <= 'Z' // In range A-Z
>>> 180:                  || (U >= 0xC0 && U <= 0XDE && U != 0xD7)) // ..or A-grave-Thorn, excl. multiplication
>>> 181:                  && U == (b2 & 0xDF); // b2 has same uppercase
>> 
>> I'm curious if the order of comparisons could alter performance to a small degree. For example, it might be interesting to compare various permutations like below to short circuit reject unequal uppercased b2
>> 
>> Suggestion:
>> 
>>          // uppercase b1 using 'the oldest ASCII trick in the book'
>>          int U = b1 & 0xDF;
>>          return (U == (b2 & 0xDF))
>>              && ((U >= 'A' && U <= 'Z') // In range A-Z
>>                  || (U >= 0xC0 && U <= 0XDE && U != 0xD7)) // ..or A-grave-Thorn, excl. multiplication
>
> Yeah, as you noticed this code is tricky and sensitive to the order of operations. I did some quite extensive exploration before ending on the current structure. This particular one seems to improve rejection somewhat at the cost of matches.
> 
> Since rejection is relatively speaking already very fast, I think we should favour fast matching here.
> 
> Results:
> 
> 
> enchmark                                  (codePoints)  (size)  Mode  Cnt     Score    Error  Units
> RegionMatchesIC.Latin1.regionMatchesIC      ascii-match    1024  avgt   15   917.796 ± 20.285  ns/op
> RegionMatchesIC.Latin1.regionMatchesIC   ascii-mismatch    1024  avgt   15     4.367 ±  0.348  ns/op
> RegionMatchesIC.Latin1.regionMatchesIC     number-match    1024  avgt   15   399.656 ± 10.703  ns/op
> RegionMatchesIC.Latin1.regionMatchesIC  number-mismatch    1024  avgt   15     4.361 ±  0.664  ns/op
> RegionMatchesIC.Latin1.regionMatchesIC       lat1-match    1024  avgt   15  1384.443 ± 22.199  ns/op
> RegionMatchesIC.Latin1.regionMatchesIC    lat1-mismatch    1024  avgt   15     4.119 ±  0.451  ns/op

Thanks for confirming

-------------

PR: https://git.openjdk.org/jdk/pull/12632