RFR: 8377223: Port fdlibm atanh to Java

[Joe Darcy]

On Wed, 18 Feb 2026 10:10:31 GMT, Anton Artemov <aartemov 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.

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PR Review Comment: https://git.openjdk.org/jdk/pull/29782#discussion_r2824380162