| // |
| // Copyright 2020 Google LLC |
| // |
| // Licensed 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 com.google.privacy.differentialprivacy.testing; |
| |
| import static com.google.common.base.Preconditions.checkArgument; |
| |
| import com.google.common.base.Supplier; |
| |
| /** Utility class providing voting mechanisms to reduce the error of randomized tests. */ |
| public final class VotingUtil { |
| |
| private VotingUtil() {} |
| |
| /** |
| * Casts a predefined number of votes to determine a majority. Stops early as soon as the majority |
| * is clear. |
| * |
| * <p>Let n be the smallest odd integer greater or equal to {@code numberOfVotes}. This method is |
| * intended to reduce the probability of error p of a randomized test by running the test n times |
| * and taking the majority vote of the results. If the individual tests are independent, the |
| * majority vote has a probability of error equal to F(floor(n/2)) where F is the CDF of a |
| * binomial distribution over n trials with a success probability of 1 - p. |
| * |
| * @param voteGenerator an interface to supply the results of a randomized test. The results are |
| * interpreted as accept votes if true and as a reject votes otherwise. |
| * @param numberOfVotes the number of eligible votes. The method ends early as soon as a majority |
| * is reached, i.e. not all votes may be cast. Moreover, in the case of an even number of |
| * votes a tie breaking vote may be cast if necessary. Note that this parameter must be |
| * positive. |
| * @return true if the majority of votes are accept, false otherwise. |
| */ |
| public static boolean runBallot(Supplier<Boolean> voteGenerator, int numberOfVotes) { |
| checkArgument(numberOfVotes > 0, "The number of votes must be positive"); |
| int acceptVotes = 0; |
| int rejectVotes = 0; |
| while (acceptVotes <= numberOfVotes / 2 && rejectVotes <= numberOfVotes / 2) { |
| if (voteGenerator.get()) { |
| acceptVotes++; |
| } else { |
| rejectVotes++; |
| } |
| } |
| return acceptVotes > rejectVotes; |
| } |
| } |