wrong results for SPACING and RRSPACING at compile time

[Paul Thomas]

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.
>
>  
>