[Bug libstdc++/89991] Complex numbers: Calculation of imaginary part is not correct

[sgk at troutmask dot apl.washington.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89991

--- Comment #25 from Steve Kargl <sgk at troutmask dot apl.washington.edu> ---
On Tue, Apr 09, 2019 at 08:24:29PM +0000, redi at gcc dot gnu.org wrote:
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89991
> 
> --- Comment #24 from Jonathan Wakely <redi at gcc dot gnu.org> ---
> Thanks for the patch, I'll test it fully tomorrow.
> 

I think the patch for complex_sqrt() is correct.  The one
for complex_pow(), I think accidently works for OP, but is
likely broken for some general regions of the complex plane.

> I'll open a separate bug for the FreeBSD issue. We could use more fine-grained
> configure checks so that most C99 math functions are enabled, even if some of
> the complex ones are missing.

libgfortran has c99_functions.c that implements missing C99 math
functions when configure cannot find one.  The implementations 
are likely to be fairly direct without much optimization,
worrying about exceptional casea, or even tested extensively.