Carry-Select Adders

One issue with basic adders is that higher digits need to wait on the carry bit before computing sum.

Carry-select adders try to speed things up by computing both possibilities: if the carry bit is zero and if the carry bit is one. It then uses a MUX to select the correct output.

This is good for adding large numbers, splitting things into blocks. While it may be faster, a disadvantage is that it may use more area.