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/*
* Copyright (C) 2020 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
* in compliance with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License
* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
* or implied. See the License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.common.math;
import com.google.common.annotations.GwtIncompatible;
import java.math.BigDecimal;
import java.math.RoundingMode;
/**
* A class for arithmetic on {@link BigDecimal} that is not covered by its built-in methods.
*
* @author Louis Wasserman
* @since 30.0
*/
@GwtIncompatible
@ElementTypesAreNonnullByDefault
public class BigDecimalMath {
private BigDecimalMath() {}
/**
* Returns {@code x}, rounded to a {@code double} with the specified rounding mode. If {@code x}
* is precisely representable as a {@code double}, its {@code double} value will be returned;
* otherwise, the rounding will choose between the two nearest representable values with {@code
* mode}.
*
* <p>For the case of {@link RoundingMode#HALF_DOWN}, {@code HALF_UP}, and {@code HALF_EVEN},
* infinite {@code double} values are considered infinitely far away. For example, 2^2000 is not
* representable as a double, but {@code roundToDouble(BigDecimal.valueOf(2).pow(2000), HALF_UP)}
* will return {@code Double.MAX_VALUE}, not {@code Double.POSITIVE_INFINITY}.
*
* <p>For the case of {@link RoundingMode#HALF_EVEN}, this implementation uses the IEEE 754
* default rounding mode: if the two nearest representable values are equally near, the one with
* the least significant bit zero is chosen. (In such cases, both of the nearest representable
* values are even integers; this method returns the one that is a multiple of a greater power of
* two.)
*
* @throws ArithmeticException if {@code mode} is {@link RoundingMode#UNNECESSARY} and {@code x}
* is not precisely representable as a {@code double}
* @since 30.0
*/
public static double roundToDouble(BigDecimal x, RoundingMode mode) {
return BigDecimalToDoubleRounder.INSTANCE.roundToDouble(x, mode);
}
private static class BigDecimalToDoubleRounder extends ToDoubleRounder<BigDecimal> {
static final BigDecimalToDoubleRounder INSTANCE = new BigDecimalToDoubleRounder();
private BigDecimalToDoubleRounder() {}
@Override
double roundToDoubleArbitrarily(BigDecimal bigDecimal) {
return bigDecimal.doubleValue();
}
@Override
int sign(BigDecimal bigDecimal) {
return bigDecimal.signum();
}
@Override
BigDecimal toX(double d, RoundingMode mode) {
return new BigDecimal(d);
}
@Override
BigDecimal minus(BigDecimal a, BigDecimal b) {
return a.subtract(b);
}
}
}
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