11.5. Carry Select adder

Note: This is a carry-select adder rather than a carry-save adder. All mentions of carry-save in this video should be replaced by carry-select. There is such a thing as a carry-save adder, but it is a whole different thing.
Carry-select adders do a very intelligent trade. They exchange area for speed. The idea is simple, if the critical path is the carry path, we might as well have two carry paths that calculate outputs apriori.

[@cburrito1000]

this is a carry select adder

[@electrontube4284]

True. Thank you for the correction. Will correct title and post notes.

[@nachiketagrawal5154]

Why do we go through the entire carry chain at the last block in fixed bit carry select? Cant we multiplex the final sum just like previous sums?
We already have the 2 possibile sums given 0 and 1 carry

[@rusty5004]

@@electrontube4284 Why do we go through the entire carry chain at the last block in fixed bit carry select? Cant we multiplex the final sum just like previous sums?
We already have the 2 possible sums given 0 and 1 carry. Shouldn't the total delay then be 5*Tcarry + 3*Tmux?