[Cfp-interest 1484] Re: complex multiplication and division

[paul zimmermann]

       Dear Damian,

> Date: Tue, 11 Feb 2020 11:31:27 +1100 (AEDT)
> From: Damian McGuckin <damianm at esi.com.au>
> 
> That really wild answer seen in your division is a compiler bug and should 
> be reported as such. I more rigorously reran your examples and I also get 
> the incorrect 1.17... with -O0 on both 4.8.5 and 9.2.1 on a XEON but the 
> correct numbers for -O1 and above. Also, on 4.4.7 on a XEON, it gets it 
> wrong at any level of optimization. It seems like it is a compiler bug 
> that was half fixed. Note that I do not see this problem on a Power9 with 
> gcc 9.1.1 running CentOS 8. It gets it right at any level of optimization. 
> I do apologize that I misreported that gcc version earlier as 9.2.1. I 
> blame my dyslexic fingers. I note also that
> 
>  	double complex x = 1.0e+200 + INFINITY * I;
>  	double complex y = INFINITY * I;
> 
> both produce NaN + INFINITY * I. So the problems are more fundamental.
> 
> Remember too that the description of this group is "IEC 60559 Floating 
> point support in C". As complex arithmetic is not covered in IEC 60559 
> (IEEE 754), it is out of scope for the CFP, even if it is of interest to 
> many of us.  Just a thought.

yes this is why I wrote in my first mail "I hope this is not off-topic".

I have reported the issue on https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60181
for those who are interested to follow-up.

Paul