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## Re: [Bug-apl] fractional power ¯8⋆÷3

**From**: |
Xiao-Yong Jin |

**Subject**: |
Re: [Bug-apl] fractional power ¯8⋆÷3 |

**Date**: |
Thu, 14 Apr 2016 23:13:55 -0500 |

>* On Apr 13, 2016, at 7:03 PM, Kacper Gutowski <address@hidden> 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