RFR: JDK-8310502 : Optimization for j.l.Long.fastUUID() [v28]

[温绍锦]

> By optimizing the implementation of java.lang.Long#fastUUID, the performance of the java.util.UUID#toString method can be significantly improved.
> 
> The following are the test results of JMH: 
> 
> Benchmark                     Mode  Cnt      Score      Error   Units
> UUIDUtilsBenchmark.new       thrpt    5  92676.550 ±  292.213  ops/ms
> UUIDUtilsBenchmark.original  thrpt    5  37040.165 ± 1023.532  ops/ms

温绍锦 has updated the pull request incrementally with one additional commit since the last revision:

  change copyright years, and rename jdk.internal.util.Hex256 to jdk.internal.digits.Hex256, and add comments.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/14578/files
  - new: https://git.openjdk.org/jdk/pull/14578/files/fe9efa6b..b81f12d1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14578&range=27
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14578&range=26-27

  Stats: 154 lines in 4 files changed: 98 ins; 53 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/14578.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14578/head:pull/14578

PR: https://git.openjdk.org/jdk/pull/14578