On Jan 13, 2009, at 3:08 AM, "burnus at gcc dot gnu dot org" <gcc-bugzi...@gcc.gnu.org
> wrote:
Found at:
http://groups.google.com/group/comp.lang.fortran/browse_thread/thread/0f1d7da66fa015c2
print *, (-2.0)**2.0
end
is invalid. gfortran should print a diagnostic for -std=f95/f2003/
f2008 as NAG
f95 does:
Error: Negative floating-point value raised to a real power
Fortran 2003 in the second sentence of the second paragraph of "7.1.8
Evaluation of Operations":
"Raising a negative-valued primary of type real to a real power is
prohibitted."
The question is whether one needs to reject it completely or only with
-std=f95. Steve (see thread) thinks the constant folding gets it wrong
(-> gives "4.0").
Current results:
- Runtime and compile time evaluation (ifort, gfortran, g95):
-2.0**2.0 = 4.0
-2.0**1.9 = NaN
- Mathematica:
-2^2 = 4, -2.0^2.0 = -4.0
2.0^1.9 = -3.73213
-2.0^1.9 will be a complex number. Maybe we can define it as taking
the real part. I don't know if that is better than generating a nan
here.
Thanks,
Andrew Pinski
--
Summary: Diagnose and treat (-2.0)**2.0 properly
Product: gcc
Version: 4.4.0
Status: UNCONFIRMED
Keywords: diagnostic
Severity: normal
Priority: P3
Component: fortran
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: burnus at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38823
