[J3] Question on overflow and run-time detection of infinity?

[Clune, Thomas L. (GSFC-6101)]

Thanks Steve.    

Cheers,

- Tom


> On Nov 23, 2018, at 10:04 AM, Steven G. Kargl <kargl at troutmask.apl.washington.edu> wrote:
> 
> On Fri, Nov 23, 2018 at 02:09:51PM +0000, Clune, Thomas L. (GSFC-6101) via J3 wrote:
>> 
>> No further calculations are ever done with relative_deviation
>> except a subsequent formatted output.   Two compilers print
>> “Infinity” as expected even when using aggressive runtime
>> checking (e.g., with NAG I am using -C=all and -ieee=stop).
>> The 3rd compiler (gfortran 8.2.0) halts at the above assignment
>> to IEEE_POSITIVE_INF with the useful, albeit undesired run-time message:
>> 
>> Program received signal SIGFPE: Floating-point exception -
>> erroneous arithmetic operation.
>> 
>> The flag that toggles is -ffpe-trap=overflow.   I can turn that
>> option off, but I would like the compile to helpfully identify
>> other bad denominators (and similar things) elsewhere in the
>> application.
>> 
>> The question:   Is not the intent of the standard to allow using
>> the IEEE functionality to return values such as Infinity without
>> halting the run while still enabling run-time checking of
>> calculations that incidentally compute erroneous operations?   
>> 
> 
> What the standard allows and what the -ffpe-trap= option does
> are of course two distinct things.  The option as the name 
> suggests will trap on a floating-point exception.  This option
> is applied globally including the runtime library.  That being
> said, the standard provides facilities for a user to manage
> the halting properties of a program.  You can use a	combination
> of IEEE_GET_MODE, IEEE_SET_MODE, IEEE_GET_HALTING_MODE, and
> IEEE_SET_HALTING_MODE to micro-management/manipulate the halting
> property as you like.  I don't know the quality of any Fortran
> processors' implmentation of these functions, so your mileage
> may vary.
> 
> 
> -- 
> Steve