Clean up Hash Functions #62176
Clean up Hash Functions #62176
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Looks good to me:)
I wonder if we could use murmur3 for string hashing too? Based on this actually pretty good stackexchange answer it should perform better than DBJ2, other benchmarks show similar results (though I am not sure how it behaves with short strings). During my experiments with different hash functions I tried to do that, but the engine crashed since it somehow broke ClassDB.
StringName makes an assumption that all encodings of a string will result with the same hash, e.g. with a It's also worth noting that Murmur3A is slower than the DJB2 algorithm for strings under ~16 characters or so. I've been doing my own tests with hashes and have yet to find a good solution that performs better than the current version. I'm currently of the impression that just using a higher-quality minimal algorithm such as FNV-1a everywhere will end up being more performant than trying to use a heavier algorithm in certain circumstances due to being easier to inline. |
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@lmurray @Geometror To be honest I think for strings DJB2 does the job. The reason I moved most stuff to murmur3 is to improve the distribution in robin hood hash tables (which are super fast, but require in exchange much better hashing than what we had, or else the empty spaces get a poor distribution in big tables. This happens specially when using sequential elements, which DJB2 kind of sucks for). But for strings it should be fine, I don't see distribution being a problem in that scenario, so I doubt it makes much sense to change. |
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Clean up and do fixes to hash functions and newly introduced murmur3 hashes in godotengine#61934 * Clean up usage of murmur3 * Fixed usages of binary murmur3 on floats (this is invalid) * Changed DJB2 to use xor (which seems to be better)
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Thanks! |
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Side note: are the new hash() functions exposed to the scripting? I need to hash a Vector3... |
It's not exposed for Vector2/3(i) specifically, but you can use the global scope method on any Variant type (which includes Vector 2/3(i)):
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Clean up and do fixes to hash functions and newly introduced murmur3 hashes in #61934