gcc replaces pow(x, 0.5) by sqrt(x). This is invalid when x is -0. Indeed,
according to ISO C99 (N1256), F.9.4.4:
pow(±0, y) returns +0 for y > 0 and not an odd integer.
So, pow(-0.0, 0.5) should return +0. But sqrt(-0.0) should return -0 according
to the IEEE 754 standard (and F.9.4.5 from ISO C99).
Testcase:
#include <stdio.h>
#include <math.h>
int main (void)
{
volatile double x = -0.0;
printf ("sqrt(-0) = %g\n", sqrt (x));
printf ("pow(-0,0.5) = %g\n", pow (x, 0.5));
return 0;
}
--
Summary: gcc replaces pow(x, 0.5) by sqrt(x), invalid when x is -
0
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: vincent at vinc17 dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43419
