Modify Teddy's match verification.#275
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jneem wants to merge 2 commits intorust-lang:masterfrom
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Modify Teddy's match verification.#275jneem wants to merge 2 commits intorust-lang:masterfrom jneem:master
jneem wants to merge 2 commits intorust-lang:masterfrom
jneem:master
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Once Teddy finds a fingerprint, it needs to check if there is really a match. The old approach was to iterate over the set bits of both 64-bit halves of the fingerprint-checking vector. The new approach first extracts a bitfield that tells which bytes of the fingerprint-checking vector are non-zero. Then it iterates over those bytes. This seems to be faster (up to about 10% in some benchmarks). It seems like the main reason that this approach is faster is that most matched fingerprints only match in one place. The new code narrows in on the important place more quickly, whereas the old code wasted time unnecessarily examining an empty u64. The gain seems to be larger with AVX2 support (which is not included in this patch). Presumably it would be even larger with AVX512.
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I rebased, squashed and merged this in 12cb63b Thanks! |
Member
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@jneem I somehow missed your comment about AVX2. Are you working on that? That'd be delicious. :-) |
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Yes, but it's in a separate crate (https://github.com/jneem/teddy), which has diverged a bit. It also implements aligned loads, which gives another 10% or so. |
This was referenced Oct 13, 2025
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Once Teddy finds a fingerprint, it needs to check if there is really a
match. The old approach was to iterate over the set bits of both 64-bit
halves of the fingerprint-checking vector. The new approach first
extracts a bitfield that tells which bytes of the fingerprint-checking
vector are non-zero. Then it iterates over those bytes. This seems to
be faster (up to about 10% in some benchmarks).
It seems like the main reason that this approach is faster is that most
matched fingerprints only match in one place. The new code narrows in
on the important place more quickly, whereas the old code wasted time
unnecessarily examining an empty u64.
The gain seems to be larger with AVX2 support (which is not included in
this patch). Presumably it would be even larger with AVX512.
Here are some benchmarks (on a Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz). I've left only the ones that actually use Teddy.
Before:
After: