[Bug fortran/15441] RRSPACING broken for denormals

["tobi at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From tobi at gcc dot gnu dot org  2004-09-14 12:59 -------
I tried this:
x = 1.
i = 0
do while (x>0.)
   x = x/2.; i = i+1
   write(*,10) i, x, rrspacing(x)
10 format("2**(-",i3,") rrspacing(",e8.2,") =",e8.2)
end do
end
the output reads:
2**(-  1) rrspacing(0.50E+00) =0.84E+07
2**(-  2) rrspacing(0.25E+00) =0.84E+07
2**(-  3) rrspacing(0.13E+00) =0.84E+07
...
2**(-147) rrspacing(0.56E-44) =0.84E+07
2**(-148) rrspacing(0.28E-44) =0.84E+07
2**(-149) rrspacing(0.14E-44) =0.84E+07
2**(-150) rrspacing(0.00E+00) =0.00E+00

Now if I understand things correctly and got my facts right, the relative
spacing should become larger once we hit denormals, because we don't have as
many digits left for recording the mantissa. More precisely, IIRC numbers with
exponent in [-149,-126] are denormals, and their relative spacing should
increase by a factor of two at every iteration of the above program, for
RRSPACING to be also meaningful in the case of denormals.

I understand that denormals are not part of the floating point model specified
in the standard, and therefore the behavior of RRSPACING is not specified for
denormals, therefore I'm changing the severity to 'enhancement', but I'm not
convinced that we're doing The Right Thing.

BTW the program compiled with ifc gives the same output as with gfortran.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=15441