1 /* 2 * Copyright (c) 2013, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 24 import java.util.*; 25 import java.util.stream.*; 26 27 /* 28 * @test 29 * @bug 8006572 30 */ 31 public class TestDoubleSummaryStatisticsSummation { 32 public static void main(String... args) { 33 double base = 1.0; 34 double increment = Math.ulp(base)/2.0; 35 int count = 1_000_001; 36 /* 37 * The exact sum of this stream is 1 + 1e6*ulp(1.0) but a 38 * naive summation algorithm will return 1.0 since (1.0 + 39 * ulp(1.0)/2) will round to 1.0 again. 40 */ 41 TestDoubleIterator tdi = new TestDoubleIterator(base, 42 increment, 43 count); 44 DoubleSummaryStatistics stats = 45 StreamSupport.doubleStream(Spliterators.spliteratorUnknownSize(tdi, 46 Spliterator.IMMUTABLE | 47 Spliterator.NONNULL), 48 false).collect(DoubleSummaryStatistics::new, 49 DoubleSummaryStatistics::accept, 50 DoubleSummaryStatistics::combine); 51 52 double expectedSum = base + (increment * (count - 1)); 53 compareUlpDifference(expectedSum, stats.getSum(), 3); 54 55 double expectedAvg = expectedSum / count; 56 compareUlpDifference(expectedAvg, stats.getAverage(), 3); 57 } 58 59 private static void compareUlpDifference(double expected, double computed, double threshold) { 60 double ulpDifference = Math.abs(expected - computed) / Math.ulp(expected); 61 62 if (ulpDifference > threshold) { 63 System.out.printf("Numerical summation error too large, %g ulps rather than %g.%n", 64 ulpDifference, threshold); 65 throw new RuntimeException(); 66 } 67 68 } 69 70 static class TestDoubleIterator implements PrimitiveIterator.OfDouble { 71 private double base; 72 private double subsequent; 73 private long count; 74 private long iteration = 0; 75 76 /** 77 * Construct a {@code TestDoubleStream} of {@code count} 78 * elements whose first value is {@code base} and whose 79 * following values are all {@code subsequent}. 80 */ 81 TestDoubleIterator(double base, double subsequent, long count) { 82 this.base = base; 83 this.subsequent = subsequent; 84 this.count = count; 85 } 86 87 @Override 88 public boolean hasNext() { 89 return (iteration < count); 90 } 91 92 @Override 93 public double nextDouble() { 94 if (iteration >= count) 95 throw new NoSuchElementException(); 96 else { 97 iteration++; 98 return (iteration == 1) ? base : subsequent; 99 } 100 } 101 } 102 }