Because it’s hashing an item of fixed size. This is specialized for 32 or 64-bit integers. clhash supports arbitrary length strings. There is a performance cost

Because it’s hashing an item of fixed size. This is specialized for 32 or 64-bit integers. clhash supports arbitrary length strings. There is a performance cost for that generality. For example, in my experiments, clhash is 1/3 as fast as murmurhash or Wang’s 64-bit hash for 64-bit integers.