There are reversible bit hash functions too. I've used twang's 64 bit mix in places where the domain is just as big as the hash space - 64 bit to 8 byte hash t

There are reversible bit hash functions too. I've used twang's 64 bit mix in places where the domain is just as big as the hash space - 64 bit to 8 byte hash to 12 byte Y64 strings. That said, the results are almost always ugly, if I had to do it again, I'd do it the way gfycat does (adjective, adjective, animal).