Digital Arithmetic

144 e H • pT E N 3 Multioperand Addition

P

3

4

5

6

7

9

11

H k W

1

4

3

10

9

7

21

T A B t t 3.1 Values of H, k, and W for typical modules.

An implementation requires the coding of the variables h and w. Then the

modules can be implemented using gate networks. Figure 3.5 shows the im-

plementation of a [4:2] module. In this case, h =

h i, i -Jr hi,2

(unary code) and

w - 2c + 2b + a, as shown in the figure.

Another possible implementation uses a network of full-adders. Such an

implementation for a [4:2] module is given in Chapter 2; Figure 3.6 illustrates

this implementation for [5:2] and [7:2] modules. ...