RFR: 8305767: HdrSeq: support for a merge() method

Fri Apr 7 23:09:40 UTC 2023

A merge functionality on stats (distributions) was needed for the remembered set scan that I was using in some companion work. This PR implements a first cut at that, which is sufficient for our first (and only) use case.

Unfortunately, for expediency, I am deferring work on decaying statistics, as a result of which users that want decaying statistics will get NaNs instead (or trigger guarantees).

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Commit messages:
 - 8298597: HdrSeq: support for a merge() method

Changes: https://git.openjdk.org/jdk/pull/13395/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13395&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8305767
  Stats: 180 lines in 5 files changed: 153 ins; 2 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/13395.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13395/head:pull/13395

PR: https://git.openjdk.org/jdk/pull/13395