Package hyperloglog implements the HyperLogLog algorithm for cardinality estimation. In English: it counts things. It counts things using very small amounts of memory compared to the number of objects it is counting.
For a full description of the algorithm, see the paper HyperLogLog: the analysis of a near-optimal cardinality estimation algorithm by Flajolet, et. al. at http://algo.inria.fr/flajolet/Publications/FlFuGaMe07.pdf
For documentation see http://godoc.org/github.com/DataDog/hyperloglog
Included are a set of fast implementations for murmurhash suitable for use on 32 and 64 bit integers on little endian machines.
$ go get github.com/DataDog/hyperloglog
$ cd $GOPATH/src/github.com/DataDog/hyperloglog
$ go test -test.v
$ go test -bench=.
hyperloglog is licensed under the MIT license.