<div><p>We prove the binary64 hyperbolic arc-tangent function from GNU libc 2.43, released end of January 2026, is correctly rounded.</p></div>

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A formal proof that the binary64 hyperbolic arc-tangent function (atanh) in GNU libc 2.43, released in January 2026, is correctly rounded according to IEEE 754 standards.

The GNU libc atanh is correctly rounded