RFR: 8353741: Eliminate table lookup in UUID.toString [v6]
Johannes Graham
duke at openjdk.org
Wed May 21 00:37:52 UTC 2025
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 469:
> 467: buf[18] = '-';
> 468: buf[23] = '-';
> 469:
I would suggest a comment here along the lines of "Although the UUID byte ordering is defined to be big-endian, LittleEndian is used here to optimize for the most common architectures. `hex8` reverses the order internally."
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PR Review Comment: https://git.openjdk.org/jdk/pull/22928#discussion_r2099081840
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