Support externally-hashed keys - #40
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Interesting... I'm trying to figure out if we could avoid switching from |
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This is ~10% faster for u64 lookups. For lookups and construction the time is constant regardless of the true length of the input (assuming you can amortize the hashing cost somehow externally to this library). For example, for a 128 byte string construction is ~2.5x faster and lookups are ~1.7x faster.
Latest rayon requires at least Rust 1.63, regex requires 1.65, and std::hint::black_box was stabilized in 1.66, so bump that. Also bump the current stable version to validate with a newer Rust since presumably that's the intention of the second version.
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I have a use-case where:
This provides savings so that the lookup within the hash function is basically the same cost as a u64 regardless of the true size of the key input. Obviously the hash still has to be done somewhere, so it's not totally free but as mentioned the savings grow the more hash functions I need to interrogate and it lets me use a faster xxh3 hash.
I tried to keep the identical hash results if you use anything other than the new ExternallyHashed type while simultaneously carving out a fast path for it to shine (I've also in theory fast-pathed construction/lookups for integer keys where we can skip constructing the WyHash state object but I didn't bother benchmarking the actual improvement there).