Population count. Design a circuit that takes as input n bits and produces as output the binary representation of the number of 1s among the inputs. Give a formula for the number of gates required by...

Population count. Design a circuit that takes as input n bits and produces as output the binary representation of the number of 1s among the inputs. Give a formula for the number of gates required by your design and draw your circuit at the gate level of abstraction for n = 4.