Counting Ones Without Broadword Operations

Abstract

A lower time bound $\Omega(\min(\nu(x), n-\nu(x))$ for counting the number of ones in a binary input word $x$ of length $n$ is presented, where $\nu(x)$ is the number of ones. The operations available are increment, decrement, bit-wise logical operations, and assignment. The only constant available is zero. An almost matching upper bound is also obtained.