Population Count
January 28, 2011
The population count of a bitstring is the number of set bits (1-bits) in the string. For instance, the population count of the number 23, which is represented in binary as 101112, is 4. The population count is used in cryptography and error-correcting codes, among other topics in computer science; some people use it as an interview question. The population count is also known as Hamming weight.
Your task is to write a function that determines the population count of a number representing a bitstring; you should concern yourself with the efficiency of your solution. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.
Programming Praxis 