Improve performance when hashing sets of state IDs. #452
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Add probe count logging to `to_set_htab_check`.
Switch from adding each PHI_64*(id+1) to xor-ing, it has better
collision behavior.
This change makes
time ./re -rpcre 'a[^bz][^bz][^bz][^b][^bz][^bz][^bz][^bz][^bz][^bz][^b][^bz][^bz][^bz][^bz][^bz]'
go from taking ~14 seconds to ~6 when I run it locally, because
adding leads to much higher probe counts on average.
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The bad hash function became noticeable while fuzzing. |
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trie of 40k 100-character random words on my desktop before: after: (I grepped out a couple of outliers, the random seed for blab produces extreme situations occasionally) So this case hits slightly differently for the local details, but the overall behaviour is the same curve. Those outliers look like this: which I've seen before. but I think we should check this hashing isn't introducing new especially bad cases somehow |
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Scott confirmed this is uniformly better |
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I was confirming that changing to xorshift* was uniformly better, but was just about to push when this got merged, so that's in a new PR. |
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Add probe count logging to
to_set_htab_check.Switch from adding each PHI_64*(id+1) to xor-ing, it has better collision behavior.Switch to xoshiro64* instead.This change makes
go from taking ~14 seconds to ~6 when I run it locally, because adding leads to much higher probe counts on average.