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

[Eirik Bjorsnos]

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 ASCII chars):

This methods 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

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Commit messages:
 - Update copyright year
 - Avoid bit shifting in the CharacterDataLatin1 fast-path

Changes: https://git.openjdk.org/jdk/pull/13040/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13040&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8304245
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/13040.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13040/head:pull/13040

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