[Bug libstdc++/50880] __complex_acosh() picks wrong complex branch

["kreckel at ginac dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50880

--- Comment #5 from Richard B. Kreckel <kreckel at ginac dot de> 2011-10-28 07:06:57 UTC ---
On 10/27/2011 11:24 AM, paolo.carlini at oracle dot com wrote:
> Thus, to understand and clarify why this has not been noticed so far, you are
> on a target which doesn't support in the underlying C library these complex
> functions, right? Because normally (eg, on Linux) these days we just forward to
> __builtin_cacosh*, the code you are touching is just a "surrogate", a
> "fallback", which doesn't get right all the special cases, NaNs, infinity.

Well, I didn't "notice" it. Searching for bugs involving branch cut 
positions of inverse trig functions in a range of FOSS projects is a pet 
project of mine.  ;-)

BTW: I noticed that my patch tests if (__z.real() < -0.0), which is 
correct, but the sign of zero looks eccentric and might potentially 
confuse future readers. I suggest removing it. It doesn't matter at all, 
anyhow.