Discussion

purplesyringa

bryanrasmussen: a hash function that produce hashes that are already in the hash table should, IMO, not be called a hash function.I get why technically it is a hash function, but still, no.

ahazred8ta: A perfect hash function https://en.wikipedia.org/wiki/Perfect_hash_function has to be specially constructed for each desired set of inputs. Generic hash functions cannot be 'perfect'.

phinnaeus: Here is a hash function that does not have hash collisions: fn hash(data): return data

Charon77: > Like additionI'm perplexed to the claim that addition is cheaper than XOR, especially since addition is built upon XOR, am I missing anything? Is it javascript specific?

Charon77: Well it no longer constrains the data in a fixed output length.

dbdr: Sure, but if you constrain to fixed output length, you will definitely have collisions (Pigeon Hole Principle). There's no way around that.

johanvts: This is a excellent article for anyone looking for some more in-depth analysis of tabulation based hashing methods: https://arxiv.org/abs/1505.01523

baruch: It is mathematically impossible for a proper hash function (one with an output range smaller than its input range) to not have collisions. The proof uses the Pigeon Hole Principle https://en.wikipedia.org/wiki/Pigeonhole_principle