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.function.*;
26 import java.util.stream.*;
27
28 /*
29 * @test
30 * @bug 8006572
31 * @summary Test for use of non-naive summation in stream-related sum and average operations.
32 */
33 public class TestDoubleSumAverage {
34 public static void main(String... args) {
35 int failures = 0;
36
37 failures += testForCompenstation();
38 failures += testZeroAverageOfNonEmptyStream();
39
40 if (failures > 0) {
41 throw new RuntimeException("Found " + failures + " numerical failure(s).");
42 }
43 }
44
45 /**
46 * Compute the sum and average of a sequence of double values in
47 * various ways and report an error if naive summation is used.
48 */
49 private static int testForCompenstation() {
50 int failures = 0;
51
52 /*
53 * The exact sum of the test stream is 1 + 1e6*ulp(1.0) but a
54 * naive summation algorithm will return 1.0 since (1.0 +
55 * ulp(1.0)/2) will round to 1.0 again.
56 */
57 double base = 1.0;
58 double increment = Math.ulp(base)/2.0;
59 int count = 1_000_001;
60
61 double expectedSum = base + (increment * (count - 1));
62 double expectedAvg = expectedSum / count;
63
64 // Factory for double a stream of [base, increment, ..., increment] limited to a size of count
65 Supplier<DoubleStream> ds = () -> DoubleStream.iterate(base, e -> increment).limit(count);
66
67 DoubleSummaryStatistics stats = ds.get().collect(DoubleSummaryStatistics::new,
68 DoubleSummaryStatistics::accept,
69 DoubleSummaryStatistics::combine);
70
71 failures += compareUlpDifference(expectedSum, stats.getSum(), 3);
72 failures += compareUlpDifference(expectedAvg, stats.getAverage(), 3);
73
74 failures += compareUlpDifference(expectedSum,
75 ds.get().sum(), 3);
76 failures += compareUlpDifference(expectedAvg,
77 ds.get().average().getAsDouble(), 3);
78
79 failures += compareUlpDifference(expectedSum,
80 ds.get().boxed().collect(Collectors.summingDouble(d -> d)), 3);
81 failures += compareUlpDifference(expectedAvg,
82 ds.get().boxed().collect(Collectors.averagingDouble(d -> d)),3);
83 return failures;
84 }
85
86 /**
87 * Test to verify that a non-empty stream with a zero average is non-empty.
88 */
89 private static int testZeroAverageOfNonEmptyStream() {
90 Supplier<DoubleStream> ds = () -> DoubleStream.iterate(0.0, e -> 0.0).limit(10);
91
92 return compareUlpDifference(0.0, ds.get().average().getAsDouble(), 0);
93 }
94
95 /**
96 * Compute the ulp difference of two double values and compare against an error threshold.
97 */
98 private static int compareUlpDifference(double expected, double computed, double threshold) {
99 double ulpDifference = Math.abs(expected - computed) / Math.ulp(expected);
100
101 if (ulpDifference > threshold) {
102 System.err.printf("Numerical summation error too large, %g ulps rather than %g.%n",
103 ulpDifference, threshold);
104 return 1;
105 } else
106 return 0;
107 }
108 }