Hashing for sparse bit vectors

Question

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%.

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.

Answer 1

Would a Bloom filter help?

If the bit vector is 2^32 bits, then why not just use a 32 bit integer?

Answer 2

I would just hash the bits as usual by calling

hash<vector<bool>>(...)

if you're using C++0x, or else see boost::hash.