
102 e H A P T E R 2 Two-Operand Addition
F I G U R E 2.33
Radix-8 carry-save adder.
The corresponding implementation is shown in Figure 2.33. Of course, this high-
radix implementation results in an increase in delay: from the delay of one full-
adder (for the radix-2 case) to the delay of a radix-r adder.
2.12~2
Signed-Digit Adder
In this case the result of the addition uses signed digits, which is a fixed-radix
representation with digit values from a signed-integer set. That is,
n--1
x "-- ~ Xi ri
2.88
0
with a digit set
D--{-b,...,-1, O, 1,...,a}
2.89
with the restriction a + b + 1 > r. Ifa + b + 1 - r, the representation ...