[Bug fortran/57749] -ffpe-trap=zero or invalid produces SIGFPE on complex zero ** 1e0

[anlauf at gmx dot de]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57749

--- Comment #5 from Harald Anlauf <anlauf at gmx dot de> ---
(In reply to Vittorio Zecca from comment #4)
> I am happy to refresh my complex analysis study of long ago.
> The singularity of log(x) in zero is not essential.

Right.

> Essential singularity means the Laurent seriesis infinite in both
> directions?
> z**-k and z**+k  roughly, but log(z) Laurent series is infinite only for
> z**+k.
> I hope to remember correctly.
> But exp(y*log(x)) may well be essential, however.

Yes, since exp(z) has an essential singularity at complex infinity.

> Anyway I am not sure this is an essential (forgive the pun) reason to raise
> an exception

So what should the correct result be?

> Also I do not understand the different behaviour with different levels of
> optimization,

I think that compile-time optimization realizes that the exponent y
is actually exactly a positive integer and does some simplification.
At -O0, you get an evaluation by the run-time library.

> and I confirm the a.out executable runs fine under valgrind.
> And the code runs fine with Intel ifort.
> And I really do not see how complex zero raised to a positive power should
> raise an exception.

Well, you actually provide a non-integer (real or complex) exponent,
even if it is accidentally a positive integer.