Re: [testsuite gfortran] partial fix for secnds*.f

[Tobias Schlüter <tobias dot schlueter at physik dot uni-muenchen dot de>]

Thomas Koenig wrote:
> On Mon, 2007-05-28 at 15:28 +0200, Dominique Dhumieres wrote:
> > Why is it so difficult to see the obvious?
> > -      dat1 = 0.001*real (values(8)) + real (values(7)) +
> > -     &        60.0*real (values(6)) + 3600.0* real (values(5))
> > +      dat1 = 3600.0* real (values(5)) + 60.0*real (values(6)) +
> > +     &       real (values(7)) + 0.001*real (values(8))
>
> Ouch.  Yes, that can make a difference.
>
> However... as a general rule, I've learned that it is better to add real
> values from small to big (less loss of precision that way).  Would it
> make more sense to change the order of terms in the secnds intrinsic?

I think we should use parentheses to enforce the order.  Not that the 
compiler reorders in its current incarnation, but it might at some 
point.  I don't know of a way to enforce an order of evaluation in C 
besides separating the addition into a series of statements or using 
volatile.

- Tobi