nfa: improve construction times for small automatons #126
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
It turns out that #121 introduced a relatively sizeable performance regression when building very small automatons. Namely, several of the steps in the construction process took worst case `O(n^2)` time, where `n` corresponds to the alphabet size (255 in this case). This ends up not being too awful when the automaton is big (a lot of patterns), but it adds fairly sizeable overhead in the case of small automatons. We fix this by making these methods take linear time instead. This makes things a little more complicated, and perhaps there is a better abstraction to make this simpler. This was found by Ruff's benchmark suite: astral-sh/ruff#6964
This mirrors the same change made for the regex crate.[1] [1]: rust-lang/regex@c788378
I added this while hacking around in the non-contiguous NFA for the 1.0.4 release and forgot to remove it. So we do a little clean-up.
|
This PR is on crates.io in |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
It turns out that #121 introduced a relatively sizeable performance regression when building very small automatons. Namely, several of the steps in the construction process took worst case
O(n^2)time, wherencorresponds to the alphabet size (255 in this case). This ends up not being too awful when the automaton is big (a lot of patterns), but it adds fairly sizeable overhead in the case of small automatons.We fix this by making these methods take linear time instead. This makes things a little more complicated, and perhaps there is a better abstraction to make this simpler.
This was found by Ruff's benchmark suite:
astral-sh/ruff#6964