zhaih commented on a change in pull request #225: URL: https://github.com/apache/lucene/pull/225#discussion_r679509373
########## File path: lucene/core/src/java/org/apache/lucene/util/automaton/NFARunAutomaton.java ########## @@ -0,0 +1,225 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.lucene.util.automaton; + +import java.util.Arrays; +import java.util.HashMap; +import java.util.Map; +import org.apache.lucene.util.ArrayUtil; +import org.apache.lucene.util.hppc.BitMixer; + +/** + * A RunAutomaton that does not require DFA, it will determinize and memorize the generated DFA + * state along with the run + * + * <p>implemented based on: https://swtch.com/~rsc/regexp/regexp1.html + */ +public class NFARunAutomaton { + + /** state ordinal of "no such state" */ + public static final int MISSING = -1; + + private static final int NOT_COMPUTED = -2; + + private final Automaton automaton; + private final int[] points; + private final Map<DState, Integer> dStateToOrd = new HashMap<>(); // could init lazily? + private DState[] dStates; + private final int alphabetSize; + + /** + * Constructor, assuming alphabet size is the whole codepoint space + * + * @param automaton incoming automaton, should be NFA, for DFA please use {@link RunAutomaton} for + * better efficiency + */ + public NFARunAutomaton(Automaton automaton) { + this(automaton, Character.MAX_CODE_POINT); + } + + /** + * Constructor + * + * @param automaton incoming automaton, should be NFA, for DFA please use {@link RunAutomaton} * + * for better efficiency + * @param alphabetSize alphabet size + */ + public NFARunAutomaton(Automaton automaton, int alphabetSize) { + this.automaton = automaton; + points = automaton.getStartPoints(); + this.alphabetSize = alphabetSize; + dStates = new DState[10]; + findDState(new DState(new int[] {0})); + } + + /** + * For a given state and an incoming character (codepoint), return the next state + * + * @param state incoming state, should either be 0 or some state that is returned previously by + * this function + * @param c codepoint + * @return the next state or {@link #MISSING} if the transition doesn't exist + */ + public int step(int state, int c) { + assert dStates[state] != null; + return step(dStates[state], c); + } + + /** + * Run through a given codepoint array, return accepted or not, should only be used in test + * + * @param s String represented by an int array + * @return accept or not + */ + boolean run(int[] s) { + int p = 0; + for (int c : s) { + p = step(p, c); + if (p == MISSING) return false; + } + return dStates[p].isAccept; + } + + /** + * From an existing DFA state, step to next DFA state given character c if the transition is + * previously tried then this operation will just use the cached result, otherwise it will call + * {@link #step(int[], int)} to get the next state and cache the result + */ + private int step(DState dState, int c) { + int charClass = getCharClass(c); + if (dState.nextState(charClass) == NOT_COMPUTED) { + // the next dfa state has not been computed yet + dState.setNextState(charClass, findDState(step(dState.nfaStates, c))); + } + return dState.nextState(charClass); + } + + /** + * given a list of NFA states and a character c, compute the output list of NFA state which is + * wrapped as a DFA state + */ + private DState step(int[] nfaStates, int c) { + Transition transition = new Transition(); + StateSet stateSet = new StateSet(5); // fork IntHashSet from hppc instead? + int numTransitions; + for (int nfaState : nfaStates) { + numTransitions = automaton.initTransition(nfaState, transition); + for (int i = 0; i < numTransitions; i++) { + automaton.getNextTransition(transition); + if (transition.min <= c && transition.max >= c) { + stateSet.incr(transition.dest); + } + } + } + if (stateSet.size() == 0) { + return null; + } + return new DState(stateSet.getArray()); + } + + /** + * return the ordinal of given DFA state, generate a new ordinal if the given DFA state is a new + * one + */ + private int findDState(DState dState) { + if (dState == null) { + return MISSING; + } + int ord = dStateToOrd.getOrDefault(dState, -1); + if (ord >= 0) { + return ord; + } + ord = dStateToOrd.size(); + dStateToOrd.put(dState, ord); + assert ord >= dStates.length || dStates[ord] == null; + if (ord >= dStates.length) { + dStates = ArrayUtil.grow(dStates, ord + 1); + } + dStates[ord] = dState; + return ord; + } + + /** Gets character class of given codepoint */ + final int getCharClass(int c) { + assert c < alphabetSize; + // binary search + int a = 0; + int b = points.length; + while (b - a > 1) { + int d = (a + b) >>> 1; + if (points[d] > c) b = d; + else if (points[d] < c) a = d; + else return d; + } + return a; + } + + private class DState { + private final int[] nfaStates; + private int[] transitions; + private final int hashCode; + private final boolean isAccept; + + private DState(int[] nfaStates) { + assert nfaStates != null && nfaStates.length > 0; + this.nfaStates = nfaStates; + int hashCode = nfaStates.length; + boolean isAccept = false; + for (int s : nfaStates) { + hashCode += BitMixer.mix(s); + if (automaton.isAccept(s)) { + isAccept = true; + } + } + this.isAccept = isAccept; + this.hashCode = hashCode; + } + + private int nextState(int charClass) { + initTransitions(); + assert charClass < transitions.length; + return transitions[charClass]; + } + + private void setNextState(int charClass, int nextState) { + initTransitions(); + assert charClass < transitions.length; + transitions[charClass] = nextState; + } + + private void initTransitions() { + if (transitions == null) { + transitions = new int[points.length]; Review comment: Right, I think this way trade memory for a faster classification of incoming characters. -- This is an automated message from the Apache Git Service. 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