Xerox 560 Reference Manual

Table 8. Condition Code Settings for Floating-Point Instructions
Condition Code
1 2 3
4 Meaning If No Trap to Location X
'
44
1
Meaning If Trap to Location X
'
44
1
Occurs
0 0 0 0
A x 0, 0/ A, or -A + A <D with FN = 1 )
*@
0 0
0
1
N < 0 Normal
*
results
0 0
1 0 N >0
*
0 1 0 0
*@
Divide by zero )
0 1 0 1
*
Overflow,
N < 0 Always trapped
0 1
1
0
*
Ov~rflow,
N >0
0 0
0
-A +A
FS=O
<D[ :
-A + A<D )
0 0
1
N < 0 > 2 P t I FN =0, and
N < OJ r
s
= I, FN=O,
os norma -
> 2 Postnorma
1- d d
} "" h"ft no underflow
0 1 0
N > 0 I ZI ng SIS
• • • an no un er-
N > 0 Izmg shifts flow with FZ= 1
1
1
0 0
Underflow wi th FZ = 0 and no trap by FS = 1 <D
*
1 1 0
1
*
1 1
1
0
*
Notes:
<D
Result set to "true" zero
@
"*" indicates impossible configurations
® Applies to add and subtract only where FN = 0
The R field of the FAL instruction must be an even value
for proper operation of the instruction; if the R field of FAL
is an odd value, the instruction traps to location X'4D',
instruction exception trap.
FSS
FLOATING SUBTRACT SHORT
(Word
index alignment)
The effective word and the contents of register R are loaded
into a set of internal registers.
FLOATING
SUBTRACT SHORT forms the two1s complement
of the effective word and then operates identically to
FLOATING
ADD SHORT (FAS). If no floating-point
arithmetic fault occurs, the difference is loaded into reg-
ister R as a short-format floating-point number.
Affected: (R), CC
(R) - EW- R
Trap: Floating-point arith-
metic fault
FSL
Underflow,
N < O}
FZ= 1
Underflow,
N
>0
FLOATING SUBTRACT LONG
(Doubleword index alignment)
The effective doubleword and the contents of registers R
and Ru 1 are loaded into a set of internal registers.
I FLOATING SUBTRACT LONG forms the two1s comple-
ment of the effective doubleword and then operates iden-
tically to FLOATING ADD LONG (FAL). If no floating-
point arithmetic fault occurs, the difference is loaded into
registers Rand Ru 1 as a long-format floating-point number.
Affected: (R), (Ru 1), CC
(R, Rul) - ED - R, Rul
Trap:
Floating-point arith-
metic fault, instruc-
tion exception
The R field of the FS L instruction must be an even value for
proper operation of the instruction; if the R field of FSL is
an odd value, the instruction traps to location X'4D',
instruction exception trap.
Floating-Point Arithmetic Instructions 79

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