RFR: JDK-8301392: Port fdlibm log1p to Java [v4]

[Raffaello Giulietti]

On Wed, 1 Feb 2023 19:19:05 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Another day, another PR to port FDLBIM to Java, this time for the log1p method.
>> 
>> Other than using the two-argument form of the __HI method in Java transliteration version rather than C macro, there are no appreciable differences between the original C source in 
>> 
>> src/java.base/share/native/libfdlibm/s_log1p.c
>> 
>> and the transliteration for testing purposes in
>> 
>> test/jdk/java/lang/StrictMath/FdlibmTranslit.java
>> 
>> The more idiomatic port in
>> 
>> src/java.base/share/classes/java/lang/FdLibm.java
>> 
>> has had a series of transformation applied layering on the transliteration. The intermediate commits show the progress.
>> 
>> The regression tests include probing around input values the implementation uses to decided which branch to take.
>
> Joe Darcy has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Improve spacing.

test/jdk/java/lang/StrictMath/Log1pTests.java line 245:

> 243:              -0x1.0p-54,
> 244:               0x1.0p-54,
> 245: 

maybe add a comment like
`/* approximations around sqrt(2)/2 - 1 and around sqrt(2) - 1 */`

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PR: https://git.openjdk.org/jdk/pull/12301