001/*
002 * Copyright (C) 2020 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.math;
016
017import com.google.common.annotations.GwtIncompatible;
018import com.google.common.annotations.J2ktIncompatible;
019import java.math.BigDecimal;
020import java.math.RoundingMode;
021
022/**
023 * A class for arithmetic on {@link BigDecimal} that is not covered by its built-in methods.
024 *
025 * @author Louis Wasserman
026 * @since 30.0
027 */
028@J2ktIncompatible
029@GwtIncompatible
030public class BigDecimalMath {
031  private BigDecimalMath() {}
032
033  /**
034   * Returns {@code x}, rounded to a {@code double} with the specified rounding mode. If {@code x}
035   * is precisely representable as a {@code double}, its {@code double} value will be returned;
036   * otherwise, the rounding will choose between the two nearest representable values with {@code
037   * mode}.
038   *
039   * <p>For the case of {@link RoundingMode#HALF_DOWN}, {@code HALF_UP}, and {@code HALF_EVEN},
040   * infinite {@code double} values are considered infinitely far away. For example, 2^2000 is not
041   * representable as a double, but {@code roundToDouble(BigDecimal.valueOf(2).pow(2000), HALF_UP)}
042   * will return {@code Double.MAX_VALUE}, not {@code Double.POSITIVE_INFINITY}.
043   *
044   * <p>For the case of {@link RoundingMode#HALF_EVEN}, this implementation uses the IEEE 754
045   * default rounding mode: if the two nearest representable values are equally near, the one with
046   * the least significant bit zero is chosen. (In such cases, both of the nearest representable
047   * values are even integers; this method returns the one that is a multiple of a greater power of
048   * two.)
049   *
050   * @throws ArithmeticException if {@code mode} is {@link RoundingMode#UNNECESSARY} and {@code x}
051   *     is not precisely representable as a {@code double}
052   * @since 30.0
053   */
054  public static double roundToDouble(BigDecimal x, RoundingMode mode) {
055    return BigDecimalToDoubleRounder.INSTANCE.roundToDouble(x, mode);
056  }
057
058  private static class BigDecimalToDoubleRounder extends ToDoubleRounder<BigDecimal> {
059    static final BigDecimalToDoubleRounder INSTANCE = new BigDecimalToDoubleRounder();
060
061    private BigDecimalToDoubleRounder() {}
062
063    @Override
064    double roundToDoubleArbitrarily(BigDecimal bigDecimal) {
065      return bigDecimal.doubleValue();
066    }
067
068    @Override
069    int sign(BigDecimal bigDecimal) {
070      return bigDecimal.signum();
071    }
072
073    @Override
074    BigDecimal toX(double d, RoundingMode mode) {
075      return new BigDecimal(d);
076    }
077
078    @Override
079    BigDecimal minus(BigDecimal a, BigDecimal b) {
080      return a.subtract(b);
081    }
082  }
083}