RFR: JDK-8310502 : Optimization for j.l.Long.fastUUID() [v22]

[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:

  add jdk.util.HexDigits, sharing cache array across multiple classes, including :
  java.lang.Long#fastUUID
  java.util.HexDigits
  java.lang.Long#toHexString(future)
  java.lang.Integer#toHexString(future)
  java.util.HexFormat(future)

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14578/files
  - new: https://git.openjdk.org/jdk/pull/14578/files/f08444f4..17a9f169

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14578&range=21
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14578&range=20-21

  Stats: 125 lines in 4 files changed: 55 ins; 33 del; 37 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