Another simpler example, not involving unions:

-----8<-----
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main(int argc, char** argv) {
double d[2];
d[0] = NAN;
d[1] = -d[0];
printf("%F\n", d[1]);
}
-----8<-----

Gives NAN on '030 & '882, '040, '060, with gcc 7.4.0 & gcc 10.3.0.

Does Linux support softfloat? That'd be one way to get proper math out of
qemu.

John

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On Wed, Dec 22, 2021 at 06:43:55PM +0000, John Klos wrote:

Another simpler example, not involving unions:

-----8<-----
#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main(int argc, char** argv) {
double d[2];
d[0] = NAN;
d[1] = -d[0];
printf("%F\n", d[1]);
}
-----8<-----

Gives NAN on '030 & '882, '040, '060, with gcc 7.4.0 & gcc 10.3.0.

The m68k PRM would seem to indicate that the FPU in both the 6888x and
the 68040 doesn't do a signed NAN. It specifically lists the sign bit
as a don't care bit for NAN while zero and infinity are both listed
as being signed quantities.

It seems to me this is expected behavior on the real hardware.

Brad Boyer
flar@allandria.com

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)