GNU libc atanh declared correctly rounded, it has been reported

What happened

It has been reported that the atanh implementation in the GNU C Library (glibc) is correctly rounded. The claim appears in a preprint archived on Inria's HAL server. Correct rounding means the library returns the floating‑point number closest to the true mathematical atanh(x) for the supported formats — no small feat given the cancellation and edge‑case nastiness near ±1 and subnormal ranges.

Why this matters

Why should you care? Because floating‑point surprises are the kind of hidden bugs that haunt numerical codebases for years. Correctly rounded elementary functions bring predictability: reproducible results across platforms, fewer “but it worked on my machine” mysteries, and stronger foundations for verified numerical software. This result, if it holds up to community scrutiny, is a quiet but meaningful win for scientists, engineers, and everyone who depends on glibc’s math library.

What now

The paper on HAL is the opening salvo — expect peer review, independent tests, and conversations in libm and distribution communities before the claim is treated as settled. It has been reported that the Inria page hosting the preprint shows the site running "Anubis version devel," a small detail that hints at the preprint’s development-stage status. Not exactly fireworks, but a solid notch on the reliability belt for one of the world’s most widely used C libraries.

Sources: hal.science, Hacker News