Add known upper limit to capture search.#217
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BurntSushi merged 1 commit intomasterfrom Apr 27, 2016
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| }; | ||
| self.captures_nfa( | ||
| MatchNfaType::Auto, slots, text, s) | ||
| MatchNfaType::Auto, slots, &text[..e], s) |
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Should this change also be applied above in the MatchType::Literal case?
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(And below in the DfaAnchoredReverse case?)
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Good catch on the literal case. For anchored reverse it won't help because if there's a match, it's guaranteed to end at the input (since the case only happens when the regex is anchored to the end of the text).
The DFA will report the end location of a match, so we should pass that along to capture detection. In theory, the DFA and the NFA report the same match locations, so this upper bound shouldn't be necessary---the NFA should quit once it finds the right match. It turns out though bounding the text has two important ramifications: 1. It will enable the backtracking engine to be used more often. In particular, the backtracking engine can only be used on small inputs and this change decreases the size of the input by only considering the match. 2. The backtracking engine must start every search by zeroing memory that is proportional to the size of the input. If the input is smaller, then this runs more quickly. We are also careful to bound the match to one additional "character" past the end of the match, so that lookahead operators work correctly.
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The DFA will report the end location of a match, so we should pass that
along to capture detection. In theory, the DFA and the NFA report the
same match locations, so this upper bound shouldn't be necessary---the
NFA should quit once it finds the right match. It turns out though
bounding the text has two important ramifications:
particular, the backtracking engine can only be used on small inputs and
this change decreases the size of the input by only considering the
match.
that is proportional to the size of the input. If the input is smaller,
then this runs more quickly.
We are also careful to bound the match to one additional "character"
past the end of the match, so that lookahead operators work correctly.
See also: #215.