RFR: 8310813: Simplify and modernize equals, hashCode, and compareTo for BigInteger [v6]

[Pavel Rappo]

On Wed, 9 Aug 2023 22:54:28 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>> Please review this PR to use modern APIs and language features to simplify equals, hashCode, and compareTo for BigInteger. If you have any performance concerns, please raise them.
>> 
>> This PR is cherry-picked from a bigger, not-yet-published PR, to test the waters. That latter PR will be published soon.
>
> Pavel Rappo has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 13 additional commits since the last revision:
> 
>  - Fix bugs in Shared.createSingle
>  - Merge branch 'master' into 8310813
>  - Group params coarser (suggested by @cl4es)
>    
>    - Splits 20 params into 3 groups: (S)mall, (M)edium and (L)arge.
>      Every testXYZ method invokes M operations, where M is the maximum
>      number of elements in a group. Shorter groups are cyclically padded.
>    - Uses the org.openjdk.jmh.infra.Blackhole API and increases
>      benchmark time.
>    - Fixes a bug in Shared that precluded 0 from being in a pair.
>  - Use better overloads (suggested by @cl4es)
>    
>    - Uses simpler, more suitable overloads for the subrange
>      starting from 0
>  - Improve benchmarks
>  - Merge branch 'master' into 8310813
>  - Restore hash code values
>    
>    BigInteger is old and ubiquitous enough so that there might be
>    inadvertent dependencies on its hash code.
>    
>    This commit also includes a test, to make sure hash code is
>    unchanged.
>  - Merge branch 'master' into 8310813
>  - Add a benchmark
>  - Merge branch 'master' into 8310813
>  - ... and 3 more: https://git.openjdk.org/jdk/compare/16b32b66...6fa3f694

Here's a status update for this PR. I'm currently benchmarking baseline against this PR and this PR plus changes in https://github.com/openjdk/jdk/pull/15197. It's a 3-way benchmark, so to speak. Its purpose is to see whether performance degradation brought by this PR to `equals` and `compareTo` can be sufficiently offset by the improved `ArraysSupport.mismatch` mechanics.

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PR Comment: https://git.openjdk.org/jdk/pull/14630#issuecomment-1673056244