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

[Hazen B. <hba...@ma...>]

On 05/11/2015 06:05 PM, Alan W. Irwin wrote:
> On 2015-05-11 16:23-0400 Hazen Babcock wrote:
>>
>> Much time passes during which I never implement this branch as
>> promised, and it looks like some more floating point exceptions have
>> crept in. More specifically I'm seeing floating point exceptions in
>> x25, x30 and x33. The problem seems to be with plgradient() when it
>> uses a software fallback gradient (I was testing with the xwin driver).
>>
>> You can pull a branch with floating point exception trapping enabled
>> for these examples here:
>> https://github.com/HazenBabcock/PLplot/tree/fpe_x25_x30_x33
>>
>> The problem is occurring in notcrossed() in plfill.c at line 2040 when
>> converting from a PLFLT to a PLINT. It looks like fxintersect and
>> fyintersect can take on values that are too large to be converted to
>> integers. Checking for this fixes the problem, but maybe this is
>> indicating some problem upstream?
>
> Hi Hazen:
>
> I am glad to hear you have created a topic branch that catches
> floating point exceptions.  However, I am not keen on pulling a PLplot
> topic branch from github for the reasons discussed in
> README.developers.  So could you either share your topic branch using
> "git format-patch" or else just push it to our official repo yourself?
> The former is preferred if the work is incomplete (i.e., does not
> include a cmake option to control when the PLPLOT_ENABLE_FLOAT_EXCEPT
> macro is #defined). Furthermore, if the work is incomplete, I can
> finish the cmake aspects of it as promised above and amend your commit
> accordingly.
>
> Once we have implemented an option to check for floating-point
> exceptions, then that means any of us should be able to confirm the
> ones you have found and find others in the future due to the continued
> evolution of our examples.  And, of course, this option should allow
> us to fix those floating-point exceptions as time permits.

Hi Alan,

Sorry, that branch was not meant for incorporation into PLplot which is 
why I did not follow accepted protocols. I thought it might make it 
easier for others to see the floating point exception problem for these 
3 examples.

I think we can enable floating point exception trapping more easily 
using the -ffpe-trap option provided by gfortran. This won't require us 
to mark up all of our C examples, though we might instead need to check 
that the fortran compiler is gfortran?

https://gcc.gnu.org/onlinedocs/gfortran/Debugging-Options.html

-ffpe-trap=invalid,zero,overflow,underflow

Compiling PLplot with this fortran flag (CMAKE_Fortran_FLAGS) "worked" 
for me in that it core dumps on the fortran equivalents of the C 
examples I mentioned above. I've attached my CMakeCache.txt file.

-Hazen