(j3.2006) F03/0084, was Re: Interp letter ballot #25

Bill Long longb
Fri May 11 23:09:46 EDT 2012

On 5/11/12 5:56 PM, Dan Nagle wrote:
> Hello,
> On May 11, 2012, at 14:48 , Bill Long wrote:
>> When you get to GPU-land, you end up returning  .false. for many of the "ieee_support..." inquiries in Clause 14.  Particularly, IEEE_SUPPORT_HALTING which is the one most people are interested in. (Among the small fraction of users who use any feature in Clause 14.)
> Most applications I've seen are coded for a combination of host
> and device.  Exactly what IEEE modes mean in a heterogeneous environment

Right.  And it is not always obvious whether a particular operation is 
happening on one or the other.

> is unclear to me.  I suspect that a great deal of work is required
> to make the contrary plainly appear.  Indeed, in an environment
> supporting asynchronous execution, the precise meaning of an exception

An exception occurs at a particular instruction in the code, not at a 
particular time.  So asynchronous, by itself, is not a killer.  (People 
have been using exceptions in MPI codes for years.)   However, with SIMD 
instructions and multiple threads, things get even less precise. 
Assuming exceptions are registered at all.

> is likewise unclear (at least to me).  Perhaps the issue can be resolved,
> but portably?

The easy solution is to just give up and say the processor does not 
support the feature.   Fortunately, the standard effectively allows that 



Bill Long                                           longb at cray.com
Fortran Technical Support    &                 voice: 651-605-9024
Bioinformatics Software Development            fax:   651-605-9142
Cray Inc./Cray Plaza, Suite 210/380 Jackson St./St. Paul, MN 55101

More information about the J3 mailing list