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nmacchws
Negative Multiply Accumulate Cross Halfword to Word Saturate Signed
PPC440x5 CPU Core User’s Manual Preliminary
Page 386 of 589
instrset.fm.
September 12, 2002
nmacchws
Negative Multiply Accumulate High Halfword to Word Saturate Signed
nprod
0:31
← –((RA)
16:31
× (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 low-order halfword of RA is multiplied by the high-order halfword of RB. The signed product is subtracted
from the contents of RT.
If the result of the subtraction can be represented in 32 bits, then RT is updated with the low-order 32 bits of
the result.
If the result of the subtraction cannot be represented in 32 bits, then RT is updated with a value which is
“saturated” to the nearest representable value. That is, if the result is less than –2
31
, then RT is updated with
–2
31
. Likewise, if the result is greater than 2
31
– 1, then RT is updated with 2
31
–1.
Registers Altered
•RT
• CR[CR0] if Rc contains 1
• XER[SO, OV] if OE contains 1
Architecture Note
This instruction is implementation-specific and programs which use this instruction may not be portable to
other PowerPC Book-E implementations. See Instruction Set Portability on page 250.
nmacchws RT, RA, RB OE=0, Rc=0
nmacchws. RT, RA, RB OE=0, Rc=1
nmacchwso RT, RA, RB OE=1, Rc=0
nmacchwso. RT, RA, RB OE=1, Rc=1
4 RT RA RB OE 238 Rc
0 6 11 16 21 22 31