Counting one’s in a stream of bits


I have to count the number of one’s in last $ m$ bits in a stream of bits and $ m \leq n,$ where $ n$ is the window size and it should take polylogarithmic space in $ n$ . I could only store last $ n$ bits and then count the number of one’s in those $ n$ bits but it takes $ O(n)$ space. How to achieve it in $ O(\log^k n)$ , $ k>0$ .
Any hint would be appreciated.