Figure 4-8.Shuffle Instruction - Lucent Technologies DSP1617 Information Manual

DSP1611/17/18/27/28/29 DIGITAL SIGNAL PROCESSOR
Instruction Set
4.5 Instruction Set
4.5.7 BMU Instructions (continued)
An alternate description of insertion covering both case 1 and 2 is the following: The bit field of width W comes
from the source aS, the other bits come from the other accumulator, and the result is placed in the destination
which is either of the accumulators.
Alternate Accumulator Set
aD = aS : aaT
Flags:
These flags are produced by the last operation in the BMU and can be used by the conditional instructions just like
DAU flags.
LMI Logical Minus—Bit 35 of the destination accumulator after the shift. If bit 35 = 1, sign is negative and LMI
is true.
LEQ Logical Equal—If all bits (35—0) of the destination accumulator after the shift are zero, LEQ is true.
LLV Logical Overflow—For left shifts, LLV is true if any significant bits are lost after the shift into the destina-
tion accumulator. For right shifts, LLV is true if the shift amount is greater than 35 bits. (Note that a logi-
cal right shift of 32 bits or greater fills the destination accumulator with zeros.)
LMV Mathematical Overflow—LMV is true if any of the bits 35—31 are different after the shift operation.
Four BMU flags are also set from the last operation:
evenp Even Parity—True if bits 35—0 have an even number of ones (zeros).
oddp Odd Parity—True if bits 35—0 have an odd number of ones (zeros).
mns1
Minus 1—True if all bits 35—0 are ones (minus 1 in two's complement).
nmns1 Not Minus 1—True for all other patterns than all ones.
4-34
(continued)
The contents of alternate accumulator aaT are replaced with the value in aS. The
contents of aD are replaced with the (old) value in aaT. A temp register is used for the
exchange to provide a true swap. All transfers are a full 36 bits. Flags are set based
on the value written to aD. This is the only instruction that can access the alternate
accumulators.
aS
SOURCE ACCUMULATOR
aD
DESTINATION ACCUMULATOR
Figure 4-8. Shuffle Instruction
DRAFT COPY
36
aaT
ALTERNATE
ACCUMULATOR
36
Lucent Technologies Inc.
Information Manual
April 1998
5-4155