Now calculate the relative performance of adders. Assume that hardware corresponding to any equation containing only OR or AND terms, such as the equations for pi and gi on page B-40, takes one time unit T. Equations that consist of the OR of several AND terms, such as the equations for c1, c2, c3, and c4 on page B-40, would thus take two time units, 2T. The reason is it would take T to produce the AND terms and then an additional T to produce the result of the OR. Calculate the numbers and performance ratio for 4-bit adders for both ripple carry and carry lookahead. If the terms in equations are further defined by other equations, then add the appropriate delays for those intermediate equations, and continue recursively until the actual input bits of the adder are used in an equation. Include a drawing of each adder labeled with the calculated delays and the path of the worst-case delay highlighted.
> Now calculate the relative
performance of adders. Assume that hardware
corresponding to any equation containing only OR or
AND terms, such as the equations for pi and gi on page
B-40, takes one time unit T. Equations that consist of
the OR of several AND terms, such as the equations for
c1, c2, c3, and c4 on page B-40, would thus take two
time units, 2T. The reason is it would take T to produce
the AND terms and then an additional T to produce the
result of the OR. Calculate the numbers and
performance ratio for 4-bit adders for both ripple carry
and carry lookahead. If the terms in equations are
further defined by other equations, then add the
appropriate delays for those intermediate equations,
and continue recursively until the actual input bits of
the adder are used in an equation. Include a drawing
of each adder labeled with the calculated delays and
the path of the worst-case delay highlighted.
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