Analog Devices ADSP-BF53x Blackfin Reference page 692

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