Re: secnds.f / secnds-1.f failures

[Jerry DeLisle <jvdelisle at verizon dot net>]

Brooks Moses wrote:
> At 10:53 AM 4/27/2007, Steve Ellcey wrote:
> > I have taken a look at the sporadic secnds.f / secnds-1.f failures
> > and I have a theory about what the problem is.
> >
> > In the libgfortran function secnds we have C code containing:
> >
> >   temp1 = 3600.0 * (GFC_REAL_4)values[4] +
> >             60.0 * (GFC_REAL_4)values[5] +
> >                    (GFC_REAL_4)values[6] +
> >            0.001 * (GFC_REAL_4)values[7];
> [...]
> > We can change the library to do things in single precision or change
> > the test to do things in double precision and I think that will fix
> > the test failures.  Any preference on which way to go?
>
> Aha!  Yes, that sounds like the sort of thing I'd expect to be causing 
> this problem.  Thanks for tracking it down.
>
> I think it probably makes more sense to leave the library code as 
> double-precision, and change the testcase to match.
>
> The difference in results is fairly minimal, but we do have experimental 
> evidence that the different precisions _do_ occasionally get different 
> results, and this function isn't ever likely to be used in a place where 
> speed is of critical importance, so I think there's no good reason to 
> change it to single precision.
In seconds.f when I define dat1 and dat2 as real*8 I no longer get the random 
failures.  Would you like me to do that patch or does someone else want to.

Jerry