1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.numbers.core;
18
19 import org.apache.commons.rng.UniformRandomProvider;
20
21 /** Class providing test utilities related to doubles.
22 */
23 final class DoubleTestUtils {
24
25 /** Utility class; no instantiation. */
26 private DoubleTestUtils() {}
27
28 /** Compute the difference in ULP between two arguments of the same sign.
29 * @param a first argument
30 * @param b second argument
31 * @return ULP difference between the arguments
32 */
33 public static int computeUlpDifference(final double a, final double b) {
34 return (int) (Double.doubleToLongBits(a) - Double.doubleToLongBits(b));
35 }
36
37 /** Construct an array of length {@code len} containing random double values with exponents between
38 * {@code minExp} and {@code maxExp}.
39 * @param len vector length
40 * @param minExp minimum element exponent value
41 * @param maxExp maximum element exponent value
42 * @param rng random number generator
43 * @return random vector array
44 */
45 public static double[] randomArray(final int len, final int minExp, final int maxExp,
46 final UniformRandomProvider rng) {
47 final double[] v = new double[len];
48 for (int i = 0; i < v.length; ++i) {
49 v[i] = randomDouble(minExp, maxExp, rng);
50 }
51 return v;
52 }
53
54 /** Construct a random double with an exponent in the range {@code [minExp, maxExp]}.
55 * @param minExp minimum exponent; must be less than {@code maxExp}
56 * @param maxExp maximum exponent; must be greater than {@code minExp}
57 * @param rng random number generator
58 * @return random double value with an exponent in the specified range
59 */
60 public static double randomDouble(final int minExp, final int maxExp, final UniformRandomProvider rng) {
61 // Create random doubles using random bits in the sign bit and the mantissa.
62 final long mask = ((1L << 52) - 1) | 1L << 63;
63 final long bits = rng.nextLong() & mask;
64 // The exponent must be unsigned so + 1023 to the signed exponent
65 final int expRange = maxExp - minExp + 1;
66 final long exp = rng.nextInt(expRange) + minExp + 1023;
67 return Double.longBitsToDouble(bits | (exp << 52));
68 }
69 }