| /* |
| * 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.datasketches.sampling; |
| |
| import static org.apache.datasketches.BoundsOnBinomialProportions.approximateLowerBoundOnP; |
| import static org.apache.datasketches.BoundsOnBinomialProportions.approximateUpperBoundOnP; |
| |
| import java.util.Random; |
| import java.util.concurrent.ThreadLocalRandom; |
| |
| /** |
| * Common utility functions for the sampling family of sketches. |
| * |
| * @author Jon Malkin |
| */ |
| final class SamplingUtil { |
| |
| /** |
| * Number of standard deviations to use for subset sum error bounds |
| */ |
| private static final double DEFAULT_KAPPA = 2.0; |
| |
| |
| private SamplingUtil() {} |
| |
| /** |
| * Checks if target sampling allocation is more than 50% of max sampling size. If so, returns |
| * max sampling size, otherwise passes through the target size. |
| * |
| * @param maxSize Maximum allowed reservoir size, as from getK() |
| * @param resizeTarget Next size based on a pure ResizeFactor scaling |
| * @return <code>(reservoirSize_ < 2*resizeTarget ? reservoirSize_ : resizeTarget)</code> |
| */ |
| static int getAdjustedSize(final int maxSize, final int resizeTarget) { |
| if (maxSize - (resizeTarget << 1) < 0L) { |
| return maxSize; |
| } |
| return resizeTarget; |
| } |
| |
| static double nextDoubleExcludeZero() { |
| double r = rand().nextDouble(); |
| while (r == 0.0) { |
| r = rand().nextDouble(); |
| } |
| return r; |
| } |
| |
| static int startingSubMultiple(final int lgTarget, final int lgRf, final int lgMin) { |
| return (lgTarget <= lgMin) |
| ? lgMin : (lgRf == 0) ? lgTarget |
| : (lgTarget - lgMin) % lgRf + lgMin; |
| } |
| |
| static double pseudoHypergeometricUBonP(final long n, final int k, final double samplingRate) { |
| final double adjustedKappa = DEFAULT_KAPPA * Math.sqrt(1 - samplingRate); |
| return approximateUpperBoundOnP(n, k, adjustedKappa); |
| } |
| |
| static double pseudoHypergeometricLBonP(final long n, final int k, final double samplingRate) { |
| final double adjustedKappa = DEFAULT_KAPPA * Math.sqrt(1 - samplingRate); |
| return approximateLowerBoundOnP(n, k, adjustedKappa); |
| } |
| |
| public static Random rand() { |
| return ThreadLocalRandom.current(); |
| } |
| } |