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

[Pavel Rappo]

On Fri, 23 Jun 2023 17:27:00 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.

Note, that along with further improvements to `equals`, commit a9cbbe5, boldly suggests dropping `&` in `hashCode` to fold its implementation into a single call to a utility method.

Now, I'm not an expert, but the `test/jdk/java/math` tests pass. To my (non-expert) opinion, `&` was also dulling down `hashCode`; but I'm eager to hear comments from those who understand that more than I do.

Perhaps this PR needs to be accompanied by benchmarks.

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PR Comment: https://git.openjdk.org/jdk/pull/14630#issuecomment-1605381393