Looking at the source code below, ompiling and linking without any extra
options, one would expect the output of execution to be:
c = nan
And that is correct for GCC on RHEL5 and SLES10, with version 4.1.2. However,
on RHEL6 and SLES11, starting with GCC version 4.3.4, the output is the
following:
c = -nan
Which doesn't make much sense, since you can't really have a negative NAN.
At the same time, when the code is compiled on RHEL5, and ran on RHEL6, the
output still shows a negative NAN. It turns out that only compiling and linking
statically (with -static) allows the results of RHEL5 to be achieved on RHEL6,
and vice versa. This tells us that the libraries are responsible for this
change.
CODE:
/* File name a.c */
int main()
{
double a = 0.0;
double c = -(a/a);
printf("c = %f\n", c);
}
COMPILE:
gcc a.c
RUN:
./a.out
EXPECTED RESULTS: (identical to previous release of GCC)
c = nan
ACTUAL RESULTS: (starting with GCC 4.3.4)
c = -nan
--
Summary: GCC library allows the use of a negative value for 'NAN'
Product: gcc
Version: 4.4.4
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: murtadha at ca dot ibm dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45620
