In a look-ahead carry generator, the carry generate function Gi and the carry propagate function Pi for
inputs Ai and Bi are given by:
Pi = Ai $\oplus$ Bi and Gi = Ai Bi
The expressions for the sum bit Si and the carry bit Ci+1 of the look-ahead carry adder are given by:
Si = Pi Ci and Ci+1 = Gi + Pi Ci, where Co is the input carry.
Consider a two-level logic implementation of the look-ahead carry generator.
Assume that all Pi and Gi are available for the carry generator circuit and that the AND and OR gates
can have any number of inputs. The number of AND gates and OR gates needed to implement the
look-ahead carry generator for a 4-bit adder with 3 2 1 0 4 S ,S ,S ,S and C as its outputs are
respectively:
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