RFR: JDK-8301392: Port fdlibm log1p to Java

[Joe Darcy]

On Tue, 31 Jan 2023 06:45:27 GMT, Andrey Turbanov <aturbanov 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.
>
> src/java.base/share/classes/java/lang/FdLibm.java line 785:
> 
>> 783:         private static double ivln10    = 0x1.bcb7b1526e50ep-2;  // 4.34294481903251816668e-01
>> 784: 
>> 785:         private static double log10_2hi = 0x1.34413509f6p-2;     // 3.01029995663611771306e-01;
> 
> Are this constants intentionally not `final` ?

No, just an oversight; I'll correct that. Thanks.

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