CityHash64 appears to be the fastest available block hashing algorithm
that is good enough for dedupe. It takes much less CPU than the CRC64
function, and avoids hash-collision problems with file formats that use
CRC64 as an integrity check on 4K block boundaries.
Extracted from git://github.com/google/cityhash with the "CRC" hash
functions (which require Intel/AMD CPU support) removed. We don't
need those, and they introduce a new (if only theoretical) build-time
dependency.
Signed-off-by: Zygo Blaxell <bees@furryterror.org>
