AMCC PPC405 - Page 289

AMCC Proprietary 289
Revision 1.02 - September 10, 2007
PPC405 Processor
nmachhws
Negative Multiply Accumulate High Halfword to Word Saturate
Preliminary User’s Manual
nmachhws
Negative Multiply Accumulate High Halfword to Word Saturate Signed
nprod
0:31
← –((RA)
0:15
x (RB)
0:15
) signed
temp
0:32
← nprod
0:31
+ (RT)
if ((nprod
0
= RT
0
) ∧ (RT
0
≠ temp
1
)) then (RT) ← (RT
0
||
31
(¬RT
0
))
else (RT)
← temp
1:32
The high-order halfword of RA is multiplied by the high-order halfword of RB. The negated signed product is
summed with the contents of RT and the sum is stored in a 33-bit temporary register.
If a result does not overflow (i.e., it is accurately representable in 32 bits), the low-order 32 bits of the temporary
register are stored in RT.
If a result overflows, the returned result is the nearest representable value. Thus, if a result is less than –2
31
, the
value stored in RT is –2
31
. Likewise, if a result is greater than 2
31
– 1, the value stored in RT is 2
31
–1.
Registers Altered
•RT
• CR[CR0]
LT, GT, EQ, SO
if Rc contains 1
• XER[SO, OV] if OE contains 1
Architecture Note
This instruction is part of the Multiply-Accumulate instruction set extensions and complies with the architectural
requirements for APUs of the PowerPC Embedded Environment. As such, it is not part of the PowerPC Architec-
ture, nor is it part of the PowerPC Embedded Environment. Programs that use this instruction may not be portable
to other implementations.
nmachhws RT, RA, RB OE=0, Rc=0
nmachhws. RT, RA, RB OE=0, Rc=1
nmachhwso RT, RA, RB OE=1, Rc=0
nmachhwso. RT, RA, RB OE=1, Rc=1
4RTRARBOE110Rc
0 6 11 16 21 22 31