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LUCENE-2717: BasicOperations.concatenate creates invariant if the RHS is the empty language 

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1026104 13f79535-47bb-0310-9956-ffa450edef68
This commit is contained in:
Robert Muir 2010-10-21 19:06:45 +00:00
parent a98050eb5a
commit c15e002d70
2 changed files with 56 additions and 0 deletions
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2
lucene/src/java/org/apache/lucene/util/automaton/BasicOperations.java
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@ -61,6 +61,8 @@ final public class BasicOperations {
static public Automaton concatenate(Automaton a1, Automaton a2) {
if (a1.isSingleton() && a2.isSingleton()) return BasicAutomata
.makeString(a1.singleton + a2.singleton);
if (isEmpty(a1) || isEmpty(a2))
return BasicAutomata.makeEmpty();
// adding epsilon transitions with the NFA concatenation algorithm
// in this case always produces a resulting DFA, preventing expensive
// redundant determinize() calls for this common case.

54
lucene/src/test/org/apache/lucene/util/automaton/TestMinimize.java Normal file
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@ -0,0 +1,54 @@
package org.apache.lucene.util.automaton;
/**
* 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.
*/
import org.apache.lucene.util.LuceneTestCase;
/**
* This test builds some randomish NFA/DFA and minimizes them.
* the minimal and non-minimal are compared to ensure they are the same.
*/
public class TestMinimize extends LuceneTestCase {
public void test() {
int num = 10000 * RANDOM_MULTIPLIER;
for (int i = 0; i < num; i++) {
Automaton a = randomishAutomaton();
Automaton b = a.clone();
MinimizationOperations.minimize(b);
assertTrue(BasicOperations.sameLanguage(a, b));
}
}
private Automaton randomishAutomaton() {
// get two random Automata from regexps
Automaton a1 = AutomatonTestUtil.randomRegexp(random).toAutomaton();
if (random.nextBoolean())
a1 = BasicOperations.complement(a1);
Automaton a2 = AutomatonTestUtil.randomRegexp(random).toAutomaton();
if (random.nextBoolean())
a2 = BasicOperations.complement(a2);
// combine them in random ways
switch(random.nextInt(3)) {
case 0: return BasicOperations.concatenate(a1, a2);
case 1: return BasicOperations.union(a1, a2);
default: return BasicOperations.minus(a1, a2);
}
}
}