The following program should print "Got a NaN":
> gcc-4.0.2 nan.c && ./a.out
Got a NaN
...but...
> gcc-4.0.2 -ffast-math nan.c && ./a.out
Ugh!
I don't think that is proper behaviour even for -ffast-math.
This came up because someone compiled Gnumeric with -ffast-math. It seems
that this option is thought of as "make my program faster" with no mention
of its meaning-altering effects by lots and lots of people out there.
#include <math.h>
#include <stdio.h>
int
main (int argc, char **argv)
{
double d;
if (sscanf ("NaN", "%lf", &d) != 1)
d = 0;
if (isnan (d))
printf ("Got a NaN\n");
else
printf ("Ugh!\n");
return 0;
}
--
Summary: Problems with -ffast-math and isnan
Product: gcc
Version: 4.0.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: terra at gnome dot org
GCC build triplet: 686-pc-linux-gnu
GCC host triplet: 686-pc-linux-gnu
GCC target triplet: 686-pc-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25975
