This repository contains an implementation in C++ of the variant of the MurmurHash3 non-cryptographic hashing function used by Apache Cassandra for partitioning.
This is incompatible with the reference implementation of MurmurHash3. If you want a fast, well-characterised non-cryptographic hash function, use that (or something compatible with it).
To be clear: you should only use this code if you need to interoperate with Cassandra's partitioning.
This code only includes the implementation of the MurmurHash3_x64_128
algorithm as this is the algorithm used by Cassandra.
Cassandra's Java implementation of Murmur3 bafflingly seems to have been written and released without any attempt to test the output against the reference implementation, a fact sheepishly admitted in the comments.
All intermediate variables which are uint64_t in the reference
implementation are Java's (signed) long type in the Cassandra
implementation. (To be fair, unsigned longs weren't available until Java
8, but this doesn't really excuse calling it "Murmur3" everywhere.)
Generally, when implementing a hash algorithm it is helpful to test your implementation against some examples (test vectors).
To assist with anyone else who ends up in my situation in the future,
I have provided 1000 test vectors, generated by
Cassandra's Java implementation. They are in the format <input key>\t<hash value 1>\t<hash value 2>\n.
This implementation has been tested against these vectors.