1 /*
2 * Copyright (C) 2020 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.math;
16
17 import com.google.common.annotations.GwtIncompatible;
18 import java.math.BigDecimal;
19 import java.math.RoundingMode;
20
21 /**
22 * A class for arithmetic on {@link BigDecimal} that is not covered by its built-in methods.
23 *
24 * @author Louis Wasserman
25 * @since 30.0
26 */
27 @GwtIncompatible
28 @ElementTypesAreNonnullByDefault
29 public class BigDecimalMath {
30 private BigDecimalMath() {}
31
32 /**
33 * Returns {@code x}, rounded to a {@code double} with the specified rounding mode. If {@code x}
34 * is precisely representable as a {@code double}, its {@code double} value will be returned;
35 * otherwise, the rounding will choose between the two nearest representable values with {@code
36 * mode}.
37 *
38 * <p>For the case of {@link RoundingMode#HALF_DOWN}, {@code HALF_UP}, and {@code HALF_EVEN},
39 * infinite {@code double} values are considered infinitely far away. For example, 2^2000 is not
40 * representable as a double, but {@code roundToDouble(BigDecimal.valueOf(2).pow(2000), HALF_UP)}
41 * will return {@code Double.MAX_VALUE}, not {@code Double.POSITIVE_INFINITY}.
42 *
43 * <p>For the case of {@link RoundingMode#HALF_EVEN}, this implementation uses the IEEE 754
44 * default rounding mode: if the two nearest representable values are equally near, the one with
45 * the least significant bit zero is chosen. (In such cases, both of the nearest representable
46 * values are even integers; this method returns the one that is a multiple of a greater power of
47 * two.)
48 *
49 * @throws ArithmeticException if {@code mode} is {@link RoundingMode#UNNECESSARY} and {@code x}
50 * is not precisely representable as a {@code double}
51 * @since 30.0
52 */
53 public static double roundToDouble(BigDecimal x, RoundingMode mode) {
54 return BigDecimalToDoubleRounder.INSTANCE.roundToDouble(x, mode);
55 }
56
57 private static class BigDecimalToDoubleRounder extends ToDoubleRounder<BigDecimal> {
58 static final BigDecimalToDoubleRounder INSTANCE = new BigDecimalToDoubleRounder();
59
60 private BigDecimalToDoubleRounder() {}
61
62 @Override
63 double roundToDoubleArbitrarily(BigDecimal bigDecimal) {
64 return bigDecimal.doubleValue();
65 }
66
67 @Override
68 int sign(BigDecimal bigDecimal) {
69 return bigDecimal.signum();
70 }
71
72 @Override
73 BigDecimal toX(double d, RoundingMode mode) {
74 return new BigDecimal(d);
75 }
76
77 @Override
78 BigDecimal minus(BigDecimal a, BigDecimal b) {
79 return a.subtract(b);
80 }
81 }
82 }