[Bug fortran/48979] FRACTION und EXPONENT return invalid results for infinity/NaN

["sgk at troutmask dot apl.washington.edu" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48979

--- Comment #5 from Steve Kargl <sgk at troutmask dot apl.washington.edu> 2011-05-12 18:47:54 UTC ---
On Thu, May 12, 2011 at 05:59:44PM +0000, burnus at gcc dot gnu.org wrote:
> > Whether this really is a bug or not depends on whether one thinks that a
> > standard-compliant Fortran program should compile without requiring special
> > options (I do).
> 
> So do I - but the question is whether it is standard conforming. NAN and INF
> are not Fortran numbers, cf. "13.4 Numeric models". Admittedly, IEEE and
> Fortran model numbers are widely mixed in the standard. However, strictly
> speaking, the IEEE functionality is only available if the relevant IEEE module
> is loaded and the feature is marked as supported.
> 

>From F2003:

Page 300:

   A program is prohibited from invoking an intrinsic procedure
   under circumstances where a value to be returned in a subroutine
   argument or function result is outside the range of values
   representable by objects of the specified type and type parameters,
   unless the intrinsic module IEEE_ARITHMETIC (section 14) is accessible
   and there is support for an infinite or a NaN result, as appropriate.

Page 364:

   The intrinsic modules IEEE_EXCEPTIONS, IEEE_ARITHMETIC, and
   IEEE_FEATURES provide support for exceptions and IEEE arithmetic.
   Whether the modules are provided is processor dependent.

1) Thomas's program does not USE IEEE_ARITHMETIC.
2) gfortran does not supply the ieee modules.

So, calling fraction() with +-Inf and NaN is, I believe,
technically non-conforming.

I agree that having consistency between constant-folding
and runtime results is desirable, I disagree on calling the
need for -fno-range-check a bug.