RFR: JDK-8302028: Port fdlibm atan2 to Java [v2]

[Joe Darcy]

On Fri, 17 Feb 2023 14:18:25 GMT, Raffaello Giulietti <rgiulietti at openjdk.org> wrote:

>> Joe Darcy 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 three additional commits since the last revision:
>> 
>>  - Update regression test.
>>  - Merge branch 'master' into JDK-8302028
>>  - JDK-8302028: Port fdlibm atan2 to Java
>
> test/jdk/java/lang/Math/Atan2Tests.java line 214:
> 
>> 212:             /*
>> 213:              * If both arguments are negative infinity, then the result is the
>> 214:              * double value closest to -3*pi/4.
> 
> Perhaps add a note explaining that high precision computation shows that `-3*PI/4.0` is indeed the `double` closest to -3*pi/4.
> Since `PI` is an approximation in the first place, and since there are other two operations (in particular, the multiplication by 3), the claim is not evident.

Note (and manual double-check) added.

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PR: https://git.openjdk.org/jdk/pull/12608