On Sat, 18 Feb 2023 19:04:24 GMT, David Schlosnagle <d...@openjdk.org> wrote:
>> This PR suggests we can speed up `StringLatin1.regionMatchesCI` by applying >> 'the oldest ASCII trick in the book'. >> >> The new static method `CharacterDataLatin1.equalsIgnoreCase` compares two >> latin1 bytes for equality ignoring case. `StringLatin1.regionMatchesCI` is >> updated to use `equalsIgnoreCase` >> >> To verify the correctness of `equalsIgnoreCase`, a new test is added to >> `EqualsIgnoreCase` with an exhaustive verification that all 256x256 latin1 >> code point pairs have an `equalsIgnoreCase` consistent with >> Character.toUpperCase, Character.toLowerCase. >> >> Performance is tested for matching and mismatching cases of code point pairs >> picked from the ASCII letter, ASCII number and latin1 letter ranges. Results >> in the first comment below. > > 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 ------------- PR: https://git.openjdk.org/jdk/pull/12632
