RFR: 8353741: Eliminate table lookup in UUID.toString [v6]

[Roger Riggs]

On Mon, 19 May 2025 23:53:07 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> Improve the performance of UUID::toString by using Long.expand and SWAR (SIMD within a register) instead of table lookup. Eliminating the table lookup can also avoid the performance degradation problem when the cache misses.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   hex8 comments

src/java.base/share/classes/java/util/UUID.java line 528:

> 526:      * <pre>
> 527:      * Input:  0x0123456789ABCDEF
> 528:      * Output: 0x3031323334353637 ('0','1','2','3','4','5','6','7' in ASCII)

Only the low 32 bits are used, the example only needs to show the input ox 0x0123457.
Or change the signature to accept an `int`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/22928#discussion_r2098745362