On OpenBSD/luna88k 8.0-beta, the following test checks
an unordered comparison with a quiet NaN:
```
#include <stdio.h>
#include <ieeefp.h>
attribute((noinline)) int
is_unordered(double a, double b)
{
return __builtin_isunordered(a, b);
}
int
main(void)
{
volatile double q = __builtin_nan("");
volatile double one = 1.0;
int v;
fp_except f;
fpsetsticky(0);
v = is_unordered(q, one);
f = fpgetsticky();
printf("unordered value=%d sticky=0x%x\n", v, (unsigned)f);
return 0;
}
```
gcc -O0 fp01-qnan.c -o fp01-qnan
./fp01-qnan
FCMP should report unordered without raising IEEE invalid for a quiet NaN.
The MC88100 User's Manual, second edition, section 2.4.5.1,
distinguishes software completion from IEEE exceptions.
The MC88110 User's Manual, section 4.3.2.4, item 2 on page 4-20,
explicitly specifies quiet NaN FCMP completion without an IEEE exception.
https://www.bitsavers.org/components/motorola/88000/MC88100_RISC_Microprocessor_Users_Manual_2ed_1990.pdf
https://www.bitsavers.org/components/motorola/88000/MC88110UM_88110_Users_Manual_1991.pdf#page=125
The expected output is
unordered value=1 sticky=0x0
Instead, the unordered check produced
unordered value=1 sticky=0x10
The comparison result is correct, but the sticky exception flags
contain FP_X_INV (0x10). The generated code uses fcmp.sdd for this
comparison.
This was observed under nono 1.8.3 emulating an MC88100.
The disk image was assembled from official OpenBSD/luna88k 8.0-beta
snapshot binaries with a BUILDINFO build date of 2026-09-15 (UTC).
The compiler was the supplied native gcc 4.2.1 20070719.
The earlier m88100_fp.S sets invalid only for signaling NaNs in its
FCMP path:
```
ASLOCAL(NaN)
bb0.n s1nan, %r12, S2sigcheck /* S1 is not a NaN */
st %r1, %r31, 0 /* save return address */
bb1 sigbit, %r5, S2sigcheck /* S1 is not a signaling NaN */
set %r2, %r2, 1<oper>
br.n S1write /* FPSR bit already set, S1 is
*/
/* made quiet, and since we */
/* always write S1 if it is */
/* a NaN, write S1 and skip */
/* rest of routine */
set %r5, %r5, 1<sigbit> /* make S1 a quiet NaN */
ASLOCAL(S2sigcheck)
bb0 s2nan, %r12, S1write /* S2 is not a NaN */
bb1 sigbit, %r7, S1write /* S2 is not a signaling NaN */
set %r2, %r2, 1<oper>
set %r7, %r7, 1<sigbit> /* make S2 a quiet NaN */
```
The 2014-06-09 C replacement m88100_fp.c uses the common fpu_compare()
helper. Its single/double-precision NaN path contains:
```
case FTYPE_SNG:
if (float32_is_nan(s1->sng)) {
if (!fcmpu || float32_is_signaling_nan(s1->sng))
^^^^^^
float_set_invalid();
cc = CC_UN;
goto done;
}
if (float32_is_nan(s2->sng)) {
if (!fcmpu || float32_is_signaling_nan(s2->sng))
^^^^^^
float_set_invalid();
cc = CC_UN;
goto done;
}
break;
case FTYPE_DBL:
if (float64_is_nan(s1->dbl)) {
if (!fcmpu || float64_is_signaling_nan(s1->dbl))
^^^^^^
float_set_invalid();
cc = CC_UN;
goto done;
}
if (float64_is_nan(s2->dbl)) {
if (!fcmpu || float64_is_signaling_nan(s2->dbl))
^^^^^^
float_set_invalid();
cc = CC_UN;
goto done;
}
break;
}
```
MC88100 FCMP passes fcmpu=0, so this condition causes invalid to be
set even for a quiet NaN. The FCMP/FCMPU exception selection for quiet
NaNs appears reversed.
kernel dmesg (on nono emulator emulating LUNA-88K):
----
Copyright (c) 1982, 1986, 1989, 1991, 1993
The Regents of the University of California. All rights reserved.
Copyright (c) 1995-2026 OpenBSD. All rights reserved. https://www.OpenBSD.org
OpenBSD 8.0-beta (GENERIC) #0: Tue Sep 15 18:09:37 JST 2026
[email protected]:/usr/src/sys/arch/luna88k/compile/GENERIC
real mem = 67104768 (63MB)
avail mem = 60502016 (57MB)
random: boothowto does not indicate good seed
mainbus0 at root: OMRON LUNA-88K, 25MHz
cpu0: M88100 rev 0xb, 2 CMMU
cpu0: M88200 (16K) rev 0x9, full Icache
cpu0: M88200 (16K) rev 0x9, full Dcache
clock0 at mainbus0: MK48T02
lcd0 at mainbus0
le0 at mainbus0: address 02:00:01:83:9a:47
le0: 32 receive buffers, 8 transmit buffers
sio0 at mainbus0: 7201a
siotty0 at sio0 channel 0 (console)
ws0 at sio0 channel 1
wskbd0 at ws0 mux 1
wsmouse0 at ws0 mux 0
xp0 at mainbus0: HD647180X I/O processor
fb0 at mainbus0: 1280x1024, 4bpp
wsdisplay0 at fb0 mux 1
wskbd0: connecting to wsdisplay0
wsdisplay0: screen 0 added (std, vt100 emulation)
spc0 at mainbus0
scsibus0 at spc0: 8 targets, initiator 7
cd0 at scsibus0 targ 5 lun 0: <NONO, SCSICD, > removable
sd0 at scsibus0 targ 6 lun 0: <NONO, SCSIHD, >
sd0: 2048MB, 512 bytes/sector, 4194304 sectors
vscsi0 at root
scsibus1 at vscsi0: 256 targets
softraid0 at root
scsibus2 at softraid0: 256 targets
boot device: sd0
root on sd0a (c71ef0b1c4b73dd3.a) swap on sd0b dump on sd0b
WARNING: clock gained 5 days
WARNING: CHECK AND RESET THE DATE!
