RFR: 8377223: Port fdlibm atanh to Java

[Anton Artemov]

On Wed, 18 Feb 2026 20:47:16 GMT, Joe Darcy <darcy at openjdk.org> wrote:

>> Hi, please consider the following changes:
>> 
>> This is a port of FDLIBM atanh method.
>
> src/java.base/share/classes/java/lang/FdLibm.java line 3631:
> 
>> 3629:      */
>> 3630:     static final class Atanh {
>> 3631:         private static final double zero = 0.0;
> 
> Earlier refactorings over Fdlibm.java removed use of "zero" and "one" in favor of having those literals in-line (JDK-8304423, etc). I think that would be a good convention to follow here as support for the new method is introduced.

Sure, addressed.

> src/java.base/share/classes/java/lang/FdLibm.java line 3639:
> 
>> 3637:             int hx,ix;
>> 3638:             /*unsigned*/ int lx;
>> 3639:             hx = __HI(x);                                        /* high word */
> 
> Nit: I'd prefer "//" style comments for the one-liners here.

Addressed.

> src/java.base/share/classes/java/lang/FdLibm.java line 3657:
> 
>> 3655:             } else
>> 3656:                 t = 0.5 * Log1p.compute((x + x)/(one - x));
>> 3657:             if (hx >= 0) {
> 
> Please consider some smaller-vertical space idiom for this, like a use of the ?: construct, etc.

Addressed.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29782#discussion_r2826806044
PR Review Comment: https://git.openjdk.org/jdk/pull/29782#discussion_r2826804023
PR Review Comment: https://git.openjdk.org/jdk/pull/29782#discussion_r2826805218