Re: [patch,fortran] Fix PR19310 unnecessary error for overflowing results

[Steve Kargl <sgk at troutmask dot apl dot washington dot edu>]

On Sun, Jun 11, 2006 at 05:24:07PM +0100, Paul Brook wrote:
> >
> > AFAIK, mpfr propagates inf and nan according to IEEE-754, so
> > the front-end should be okay.  I have insufficient knowledge
> > of what the middle-end and backend do with these values.
> > I did submit a PR 24581 about problems with C99's complex type
> > and these special values.  Joseph Meyer seems to disagree
> > with my analysis of the problem.
> 
> Are we sure we have inf or nan at this point? ie. do the MPFR arithmetic 
> routines always generate inf when a calculation overflows the range of the 
> corresponding fortran type?

mpfr is designed to maintain the requested precision by extending
the range if necessary.  This is the reason why we have the kludge
for subnormal numbers, which I tried fixing by requiring verion
2.2.0.  You can explicitly set the range (emin, emax), but ISTR that
the docs mentioned this could cause problems.

> If they do then I'm happy. If not I think we should be doing that saturation 
> in gfc_check_range. Ending up with "too big" finite values is what I want to 
> avoid.

I see.  In gfc_check_real_range, we have 

  if (mpfr_sgn (q) == 0)
    retval = ARITH_OK;
  else if (mpfr_cmp (q, gfc_real_kinds[i].huge) > 0)
    retval = ARITH_OVERFLOW;
  else if (mpfr_cmp (q, gfc_real_kinds[i].subnormal) < 0)
    retval = ARITH_UNDERFLOW;
  else if (mpfr_cmp (q, gfc_real_kinds[i].tiny) < 0)

Jerry would place his disabling of range checking above this 
block.  However, we probably want to explicit set overflow
values to Inf, so the checking should look like


  if (mpfr_sgn (q) == 0)
    retval = ARITH_OK;
  else if (mpfr_cmp (q, gfc_real_kinds[i].huge) > 0)
    {
       if (disable-checking) 
         {
            set x to inf with the proper sign
            retval = ARITH_OK;
         }
       else
         retval = ARITH_OVERFLOW;
    }
  else if (mpfr_cmp (q, gfc_real_kinds[i].subnormal) < 0)
    retval = ARITH_UNDERFLOW;
  else if (mpfr_cmp (q, gfc_real_kinds[i].tiny) < 0)

-- 
Steve