[Bug c++/64497] std::scalbln does not round correctly for long doubles

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64497

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Walter Mascarenhas from comment #2)
> What if there is a difference in the expected behavior
> for this function in  C and C++11?

There isn't any difference, so it doesn't matter.

> Is it not up to g++
> for implementing what is mandated in C++11? (This
> is not a rhetorical question, I really do not know the answer.)

Yes.

> On the other hand,
> http://en.cppreference.com/w/cpp/numeric/math/scalbn states that
> 
> "If a range error due to underflow occurs, the correct result (after
> rounding) is returned."

The C++ standard doesn't say that.

> I looked at the standard (N3797.pdf) but did not find anything
> specific about std::scalbln.

It says it is the same as C, so cppreference.com is wrong.