Here's the responce from the OpenBSD folks. It seems that turning on a
define prior to the atan2() call will set the flags correctly for OpenBSD.
My guess is that NetBSD will behave similarly.
> >Number: 4154
> >Category: library
> >Synopsis: atan2(-0.0, -0.0) returning incorrect result
Our libm is compiled in multi mode and defaults to posix mode, which
sets errno and returns 0 if both args are (+-)0.0. IEEE mode does what you
want.
Check lib/libm/Makfile and lib/lib/src/{e,w}w_atan2.c for some background
info.
If you force libm to IEEE mode, you'll get the expected results:
(on macppc, same results on i386):
[EMAIL PROTECTED]:9]$ cat x.c
#include <errno.h>
#include <stdio.h>
#include <math.h>
int main() {
double res;
_LIB_VERSION = _IEEE_;
errno = 0;
res = atan2(0.0, 0.0);
perror("atan2");
printf("atan2(0.0, 0.0) = %f\n", res);
errno = 0;
res = atan2(-0.0, 0.0);
perror("atan2");
printf("atan2(-0.0, 0.0) = %f\n", res);
errno = 0;
res = atan2(0.0, -0.0);
perror("atan2");
printf("atan2(0.0, -0.0) = %f\n", res);
errno = 0;
res = atan2(-0.0, -0.0);
perror("atan2");
printf("atan2(-0.0, -0.0) = %f\n", res);
}
[EMAIL PROTECTED]:10]$ a.out
atan2: Undefined error: 0
atan2(0.0, 0.0) = 0.000000
atan2: Undefined error: 0
atan2(-0.0, 0.0) = 0.000000
atan2: Undefined error: 0
atan2(0.0, -0.0) = 3.141593
atan2: Undefined error: 0
atan2(-0.0, -0.0) = -3.141593
[EMAIL PROTECTED]:11]$
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