RFR: 8302871: Speed up StringLatin1.regionMatchesCI [v7]

[Alan Bateman]

On Tue, 21 Feb 2023 11:14:13 GMT, Eirik Bjorsnos <duke at 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.
>
> Eirik Bjorsnos has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove whitespace following '('

src/java.base/share/classes/java/lang/CharacterDataLatin1.java.template line 163:

> 161:         return mapChar;
> 162:     }
> 163:     /**

I assume you should insert a blank line between the two methods.

src/java.base/share/classes/java/lang/CharacterDataLatin1.java.template line 175:

> 173:          }
> 174:          // uppercase b1 using 'the oldest ASCII trick in the book'
> 175:          int U = b1 & 0xDF;

I'm sure some people reading this comment will wonder which book :-) It might be better to drop that bit and if possible, find a better name for "U" as normally variables start with a lower case.

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