http://www.circuitstoday.com/half-adder-and-full-adder

Half Adder

Full adder
(Can be built with two half adders and an OR gate)

A CHAIN of full adders can add any number of bits together;
Even Charles Babbage realized there is a delay in adding long strings of bits together;
A Carry Look Ahead adder is faster.
https://en.wikipedia.org/wiki/Carry-lookahead_adder
Most computers have special math co-processors for fancy math.