[Bug libstdc++/58625] std::signbit always converts to double

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58625

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
That said, I'd say that every conversion to double that would change the sign
looks wrong to me, no matter of what the rounding mode is, except perhaps for
NaN canonicalization and that sNaN could be signalled.  So IMHO this is mostly
an optimization thing, not correctness.