RFR: 8284493: Improve computeNextExponential tail performance and accuracy [v16]

[Chris Hennick]

On Wed, 7 Dec 2022 20:25:53 GMT, Xin Liu <xliu at openjdk.org> wrote:

>> It's probably just a statistical fluke involving a very large return value, but to know for sure I'd need a way to gather statistics about the return values and how they correlate with running-time outliers.
>
>> It's probably just a statistical fluke involving a very large return value, but to know for sure I'd need a way to gather statistics about the return values and how they correlate with running-time outliers.
> 
> Yeah, it's likely that p100 data are outliers. I think average and p50 data make more sense. 
> I am not a reviewer and lack domain-specific knowledge in the algorithm. I check your code and it seems reasonable. We need reviewers to look into it.

@navyxliu p50 isn't meaningful, because this change doesn't make a difference in the ~98% of cases where only the lookup table is used. It only affects the tails.

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PR: https://git.openjdk.org/jdk/pull/8131