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

[Joe Darcy]

On Fri, 17 Feb 2023 13:48:32 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/StrictMath/FdlibmTranslit.java line 480:
> 
>> 478:                     switch(m) {
>> 479:                     case 0: return  zero  ;     /* atan(+...,+INF) */
>> 480:                     case 1: return -1.0*zero  ; /* atan(-...,+INF) */
> 
> The file in the [netlib repo](https://netlib.org/fdlibm/e_atan2.c) has `-zero` rather than `-1.0*zero`.

Yes; well-observed -- that change was made back in the JDK's copy of FDLIBM back in JDK 5.0 to contend with bugs in C compilers, JDK-4984407.

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