Error Report

[Juergen Sauermann]

Hi,

I habe received the error report below on the bug-apl mailing list.

But the problem seems to be with the g++ compiler.

The effect is that -8 to the 1/3-power (= cubic root of -8) gives the
correct result when compiled with -O2, but 0 with -O5.

See http://lists.gnu.org/archive/html/bug-apl/2016-04/index.html for the
entire thread.

Best Regards,
Jürgen Sauermann

> On Apr 13, 2016, at 7:03 PM, Kacper Gutowski<mwga...@gmail.com> wrote:
>
> On Thu, Apr 14, 2016 at 1:54 AM, Xiao-Yong Jin wrote:
>> Exactly so. ‘-Ofast -fno-finite-math-only’ gives correct results.
>> What’s going on here? I don’t expect this has anything to do with NaN or Inf.
> pow(-8., 1./3) is nan.
> And -ffinite-math-only eliminates isfinite check at FloatCell.cc:422.

That explains it. Thanks.

Here is some amusement:

g++ -Ofast -fno-unsafe-math-optimizations:
pow(-8., 1./3.) => nan
isfinite => 1

g++ -Ofast -fno-unsafe-math-optimizations -fno-finite-math-only:
pow(-8., 1./3.) => nan
isfinite => 0

g++ -Ofast -fno-finite-math-only:
pow(-8., 1./3.) => -2
isfinite => 1

clang++ -march=native -Ofast:
pow(-8., 1./3.) => nan
isfinite => 0