Re: GFortran Flush (Denormals) to Zero Flag

[Jerry DeLisle <jvdelisle at verizon dot net>]

Nick K wrote:
> Jerry,
>  
> Thanks for your reply!  I isolated the flags, -ffast-math does the same thing for me like -funsafe-math-optimizations.  My test program is:
>  
>  
>       program main
>       real a,b,c
>       a=1e-20
>       b=a**2
>       print *,b
>       a=0
>       b=0
>       c=a/b
>       print *,c
>       end
>  
>  
> And the output shows that without optimization, -funsafe-math-optimizations does what I want it to, while a combination of -funsafe-math-optimizations and -O2 does the exact opposite:
>  
> root@nick-desktop:/home#
> root@nick-desktop:/home#
> root@nick-desktop:/home# gfortran -mfpmath=sse -msse2 -ffpe-trap=invalid,zero,overflow -fbounds-check -funsafe-math-optimizations test.for 
> root@nick-desktop:/home# ./a.out
>    0.0000000    
> Floating point exception
> root@nick-desktop:/home# rm ./a.out
> root@nick-desktop:/home# gfortran -mfpmath=sse -msse2 -ffpe-trap=invalid,zero,overflow -fbounds-check -funsafe-math-optimizations -O2 test.for 
> root@nick-desktop:/home# ./a.out
>   9.99994610E-41
>              NaN
> root@nick-desktop:/home# rm ./a.out
> root@nick-desktop:/home# 
>  

You may also want to try some negations like -fno-some-flag.

Jerry