2 * Copyright (C) 2015, United States Government, as represented by the
3 * Administrator of the National Aeronautics and Space Administration.
6 * The Java Pathfinder core (jpf-core) platform is licensed under the
7 * Apache License, Version 2.0 (the "License"); you may not use this file except
8 * in compliance with the License. You may obtain a copy of the License at
10 * http://www.apache.org/licenses/LICENSE-2.0.
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
18 package gov.nasa.jpf.util;
20 import java.util.NoSuchElementException;
23 * a generator for pair-wise permutations, which only considers permutations
24 * for each pair of elements, regardless of position. This reduces the
25 * number of generated permutations from N! to sum(i=1..N){N-i} + 1.
26 * This can be used to test order dependencies between two concurrent
27 * entities (threads, state machines etc), based on the same assumptions
28 * that are used in pair-wise testing
30 public class PairPermutationGenerator extends PermutationGenerator {
34 public PairPermutationGenerator (int nElements){
45 public static long computeNumberOfPermutations (int n){
47 for (int l=1; l<n; l++){
54 protected long computeNumberOfPermutations(){
55 return computeNumberOfPermutations(nElements);
60 int n = permutation.length;
62 if (nGenerated == 0){ // the initial order
66 } else if (nGenerated > 1){
67 if (nGenerated == nPermutations){
68 throw new NoSuchElementException();
70 swap(permutation, i, j); // revert last permutation
76 throw new NoSuchElementException();
82 swap(permutation, i, j);