Log message:
Initial import of Google SparseHash, an extremely memory-efficient hash_map
implementation. with 2 bits/entry overhead!

The Google SparseHash project contains several hash-map implementations in use
at Google, with different performance characteristics, including an
implementation that optimizes for space and one that optimizes for speed.

SparseHash is a template library; there are no binaries to install.

SparseHash is distributed under the terms of the BSD License.