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

[Y. Srinivas Ramakrishna]

On Fri, 7 Apr 2023 23:03:02 GMT, William Kemper <wkemper at openjdk.org> wrote:

> 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).

src/hotspot/share/utilities/numberSeq.cpp line 125:

> 123:   assert(abs2._alpha == _alpha, "Caution: merge incompatible?");
> 124: 
> 125:   // Until JDK-... is fixed, we taint the decaying statistics

JDK-... -> JDK-8298902

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PR Review Comment: https://git.openjdk.org/jdk/pull/13395#discussion_r1173946779