Hi Morten, Joseph, On 2026-01-29T13:08:43-0500, Morten Welinder wrote: > For NaN, it comes down to the ieee spec. Ieee-754-2008 in Section 6.3 > specifies that the only operations delivering a defined sign for NaNs > are: copy, abs, negate, and copysign. "For all other operations, this > standard does not specify the sign bit of a NaN result, even when > there is only one input NaN, or when the NaN is produced from an > invalid operation." > > The glibc people have in the past defended the freedom to return > whatever sign on NaN they feel like. See > https://sourceware.org/bugzilla/show_bug.cgi?id=31104 for an example > where float/double/long double versions of various functions disagree > on what sign to return for NaN. > > I don't think the man page should promise more than some standard > requires unless the implementation is specifically offering further > guarantees. Agree. Would you want to send a patch? Have a lovely night! Alex > > M. --