title: Hashing for sparse bit vectors
body: <p>Does anyone have any good intuition for a good hash function for a sparse bit vector?
  To give a concrete example, say I want to hash a 4096 bit integer where the probability of each bit being 1 is 10%.</p>
  
  <p>I want to get some compression in the hash. For example 4096 bits in and 32 bits out. This is just an example to illustrate what I am looking for. Of course, all answers are very much appreciated.</p>