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Thomas Poppe commented on LUCENE-7921: -------------------------------------- Thanks for your comment Dawid. One more think I would like to note: the second case also takes more memory and CPU to convert to an automaton, so there might be an opportunity to optimize. > More efficient way to transform a RegExp to an Automaton > -------------------------------------------------------- > > Key: LUCENE-7921 > URL: https://issues.apache.org/jira/browse/LUCENE-7921 > Project: Lucene - Core > Issue Type: Improvement > Affects Versions: 6.5.1 > Reporter: Thomas Poppe > Priority: Minor > > Consider the following example: > {code:title=ToAutomatonExample.java|borderStyle=solid} > public static void main(String[] args) { > org.apache.lucene.util.automaton.RegExp regExp = > new > org.apache.lucene.util.automaton.RegExp("[a-z]{1,13}x[a-z][a-z]?[a-z]?[a-z]?[a-z]?[a-z]{0,8}"); > org.apache.lucene.util.automaton.Automaton automaton = > regExp.toAutomaton(); > System.out.println("states: " + automaton.getNumStates()); > System.out.println("transitions: " + automaton.getNumTransitions()); > System.out.println("-------------------------------"); > try { > regExp = new > org.apache.lucene.util.automaton.RegExp("[a-z]{1,13}x[a-z]{1,13}"); > automaton = regExp.toAutomaton(); > System.out.println("Will not happen..."); > } catch > (org.apache.lucene.util.automaton.TooComplexToDeterminizeException e) { > automaton = regExp.toAutomaton(1_000_000); > System.out.println("states: " + automaton.getNumStates()); > System.out.println("transitions: " + > automaton.getNumTransitions()); > System.out.println("-------------------------------"); > } > } > {code} > Both regular expressions are equivalent, but it's much more efficient to > "unroll" the repetition. It might be possible to optimize the > Regex#toAutomaton() method to handle this repetition without going over the > default number of determinized states, and using less memory and CPU? -- This message was sent by Atlassian JIRA (v6.4.14#64029) --------------------------------------------------------------------- To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org For additional commands, e-mail: dev-h...@lucene.apache.org