Re: [Plplot-devel] floating point exception in example 29

[Tom K. <tom...@ve...>]

On Wed, May 13, 2015 at 5:01 PM, Hazen Babcock <hba...@ma...> wrote:

> On 05/13/2015 03:58 PM, Alan W. Irwin wrote:
> > In my case the only fortran compiler available is gfortran so I don't
> > need to choose that.  So instead of the above I set
> >
> > export FFLAGS='-g -ffpe-trap=invalid,zero,overflow,underflow'
> >
> > before calling cmake and building the x29f95 and ps targets.
> >
> > After that, I got the following result
> >
> > software@raven> examples/f95/x29f -dev psc -o test.psc
> >
> > Program received signal SIGFPE: Floating-point exception - erroneous
> > arithmetic operation.
> > [...]
> >
> > So I confirm there is a floating-point issue for that example, and
> > this should be easy for anyone else here to confirm that has access to
> > gfortran.  However, I am completely tied up with other PLplot issues
> > so I would appreciate it if you pursued and fixed all floating-point
> > issues revealed by this method.  But if you are too busy to do that
> > yourself, please let this list know so others with more time will be
> > motivated to take a crack at it.
>
> The problem seems to come from line 267 in this example. It looks like
> the "sec" argument is not getting passed to the C library correctly? 0.0
> becomes something like 4.2439915819305446e-314, which I think causes the
> later problems. Perhaps there is something wrong with the fortran
> bindings for plctime? I would appreciate it if a fortran expert could
> take a look.
>
> -Hazen
>
>
I would look into setting the DAZ and FTZ bits for the floating point unit.
Intel fortran has an -ftz option (can't remember how to do DAZ).  For an
example of how to do ftz in code, see:

http://geoweb3.princeton.edu/~luet/specfem3d_globe/src/shared/force_ftz.c

Tom