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

[Claes Redestad]

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/d5d285cb...6fa3f694

This looks good, thanks for the microbenchmark updates.

Your work on this PR was what prompted me to look at `ArraysSupport.mismatch` performance. The patch in #15197 should mitigate at least some of the overhead we've seen on small `BigInteger` objects on `equals` and `compareTo` micros

test/micro/org/openjdk/bench/java/math/Shared.java line 82:

> 80:         }
> 81:         int nBytes = (nBits + 7) / 8;
> 82:         var r = new Random();

Some have a preference for providing a seed for `Random` instances in micros. Either hard-coded or through a `@Param` (I find this a bit excessive). Doing so might reduce run-to-run noise.

-------------

Marked as reviewed by redestad (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/14630#pullrequestreview-1570712845
PR Review Comment: https://git.openjdk.org/jdk/pull/14630#discussion_r1289313113