Calculate the relative speed of a 64-bit adder using ripple carry only, a ripple carry of 4-bit groups that use carry lookahead, and a ripple carry of 16-bit groups that use carry lookahead

Let us take a slightly different example to understand the notion of relative speed. If A walks at 4 Km/hr and B walks at 6 Km/hr, then relative speed of A with respect to B will be 4/6 and B's speed relative to A will be 6/4.

The problem is simply asking us to use the mentioned simulator and compare the time taken by different adders (adder configurations) to produce the sum of two 64-bit numbers.

Please Note that timings computed are not dependent on the value of input numbers but the number-of-bits constituting the number, so computation of "0 + 0" will take same amount of time as for "1million + 1million".

However note that timings produced are function of various delays associated with respective adders - change those delay values and you will change the time taken to sum same numbers (by same I mean number of bits constituting the number).

Using default delay values for concerned adders at http://www.ecs.umass.edu/ece/koren/arith/simulator/ , we get following timings for adding two 64-bit numbers (time taken to generate all the sum bits or sum delay) -

(A) 64-bit adder using ripple carry only = 122.5 units
(B) ripple carry of 4-bit groups that use carry lookahead = 19.2 units
(C) ripple carry of 16-bit groups that use carry lookahead = 14.2 units

So, with default delay values used in simulator, we can compute various relative speeds as below -

A vs B = 122.5 / 19.2
B vs A = 19.2 / 122.5

A vs C = 122.5 / 14.2
B vs C = 19.2 / 14.2