RFR: 8283892: Compress and expand bits [v2]

[Paul Sandoz]

On Thu, 7 Apr 2022 14:01:53 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Paul Sandoz has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Doc and test updates.
>
> I experimented with this and drafted a few microbenchmarks along and a micro-optimization to the expand methods (see #8146). Up to you, but I think it makes sense to consider such optimizations to the plain java implementation given that 1) not all platforms have specialized instructions where an intrinsic will make sense and 2) it appears to be a boost to warmup.

@cl4es thanks, your changes to `expand` looks reasonable, given the array allocation cost.

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PR: https://git.openjdk.java.net/jdk/pull/8115