AddBytes64 adds the hash of b to the precomputed hash value h.

AddString64 adds the hash of s to the precomputed hash value h.

AddUint64 adds the hash value of the 8 bytes of u to h.

HashBytes64 returns the hash of u.

HashString64 returns the hash of s.

HashUint64 returns the hash of u.

Init64 is what 64 bits hash values should be initialized with.