Analog Devices ADSP-BF53x Blackfin, Reference

Page: 692 / 1042

Instruction Overview
19-4 ADSP-BF53x/BF56x Blackfin Processor Programming Reference
Functional Description
The Add on Sign instruction performs a two step function, as follows.
1. Multiply the arithmetic sign of a 16-bit half-word number in
src0
by the corresponding half-word number in
src1
. The arithmetic
sign of
src0
is either (+1) or (–1), depending on the sign bit of
src0
. The instruction performs this operation on the upper and
lower half-words of the same data registers.
The results of this step obey the signed multiplication rules sum-
marized in
Table 19-1 . Y is the number in
src0
, and Z is the
number in
src1
. The numbers in
src0
and
src1
may be positive or
negative.
Note the result always bears the magnitude of Z with only the sign
affected.
2. Then, add the sign-adjusted
src1
upper and lower half-word
results together and store the same 16-bit sum in the upper and
lower halves of the destination register, as shown in
Table 19-2 and
Table 19-3 .
The sum is not saturated if the addition exceeds 16 bits.
Table 19-1. Signed Multiplication Rules
SRC0 SRC1 Sign-Adjusted SRC1
+Y +Z +Z
+Y –Z –Z
–Y +Z –Z
–Y –Z +Z