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Fig. 7.11
Copying data
to the A-input of the adder
Fig. 7.12
Accumulating
another addend to the sum
applied to B
b
1
b
0
are held to the B-inputs in the figure so that the reversible
adder forms a sum. The qubits holding b
N1
...
The b
N1
...
b
1
b
0
are replaced with, and are
going to hold the accumulation. After the addition, the A-inputs are set to zero by
the controlled NOT gates on the right. Note that the a
N
...
a
1
a
0
continue to exist in
the simulated qubits where they are stored, so information is not lost.
At
this point,
the sum consists of the addition of two weighting factors,
a
N1
...
b
1
b
0
.
The next set of weighting factors are now copied to the A-inputs. For instance, if
d
N1
...
a
1
a
0
and b
N1
...
d
1
d
0
is next, an operation as in Fig.
7.12
will be carried out. After the
addition, the d
N1
...
d
1
d
0
will continue to store their weighting factors, so infor-
mation is not lost. Pursuing this method, all weighting factors from all important
attributes can be added to calculate a priority for a given image register.
Several Adders Are Required
The priority calculations can be diagrammed as in Fig.
7.13
. To begin, weighting
factors a and b are added to produce S
1
. Then d is added to produce S
2
, and so on
until the last z
P
is added to produce S
P1
, which is the net priority.
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