Re: wrong results for SPACING and RRSPACING at compile time

[Paul Thomas <paulthomas2 at wanadoo dot fr>]

Steve Kargl wrote:

> On Sun, Oct 01, 2006 at 04:15:35PM +0200, Dominique Dhumieres wrote:
>  
>
> > The following code
> >
> > real x, xd, xu
> > x = -3.0*epsilon(x)
> > xd = abs(fraction(x))*set_exponent(real(radix(x), kind=kind(x)), 1+digits(x))
> > print *, -3.0*epsilon(1.0)-x
> > print *, x, spacing(x), spacing(-3.0*epsilon(1.0))
> > print *, x, xd, rrspacing(x), rrspacing(-3.0*epsilon(1.0))
> > end
> >
> > gives
> >
> >   0.000000    
> > -3.5762787E-07  2.8421709E-14  5.6843419E-14
> > -3.5762787E-07  1.2582912E+07  1.2582912E+07   6291456.    
> >
> > where the last column of the two last lines computed from
> > spacing(-3.0*epsilon(1.0)) and rrspacing(-3.0*epsilon(1.0))
> > (hence the 'compile time' in the subject) do not match the
> > values computed through a variable.
> >
> >    
>
> Dominique,
>
> I've looked at this a little bit and I think I have the 
> the handling of subnormal numbers worked out.  However,
> I think gfortran's constant folding of spacing and rrspacing 
> may be broken for special cases.  I need to go read the
> standard for these intrinsics.
>
>