LongSum.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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 org.apache.commons.statistics.descriptive;
import java.math.BigInteger;
/**
* Returns the sum of the available values.
*
* <ul>
* <li>The result is zero if no values are added.
* </ul>
*
* <p>This class uses an exact integer sum. The exact sum is
* returned using {@link #getAsBigInteger()}. Methods that return {@code int} or
* {@code long} primitives will raise an exception if the result overflows.
*
* <p>Note that the implementation does not use {@code BigInteger} arithmetic; for
* performance the sum is computed using primitives to create a signed 128-bit integer.
* Support is provided for at least 2<sup>63</sup> observations.
*
* <p>This class is designed to work with (though does not require)
* {@linkplain java.util.stream streams}.
*
* <p><strong>This implementation is not thread safe.</strong>
* If multiple threads access an instance of this class concurrently,
* and at least one of the threads invokes the {@link java.util.function.LongConsumer#accept(long) accept} or
* {@link StatisticAccumulator#combine(StatisticResult) combine} method, it must be synchronized externally.
*
* <p>However, it is safe to use {@link java.util.function.LongConsumer#accept(long) accept}
* and {@link StatisticAccumulator#combine(StatisticResult) combine}
* as {@code accumulator} and {@code combiner} functions of
* {@link java.util.stream.Collector Collector} on a parallel stream,
* because the parallel implementation of {@link java.util.stream.Stream#collect Stream.collect()}
* provides the necessary partitioning, isolation, and merging of results for
* safe and efficient parallel execution.
*
* @since 1.1
*/
public final class LongSum implements LongStatistic, StatisticAccumulator<LongSum> {
/** Sum of the values. */
private final Int128 sum;
/**
* Create an instance.
*/
private LongSum() {
this(Int128.create());
}
/**
* Create an instance.
*
* @param sum Sum of the values.
*/
private LongSum(Int128 sum) {
this.sum = sum;
}
/**
* Creates an instance.
*
* <p>The initial result is zero.
*
* @return {@code LongSum} instance.
*/
public static LongSum create() {
return new LongSum();
}
/**
* Returns an instance populated using the input {@code values}.
*
* <p>When the input is an empty array, the result is zero.
*
* @param values Values.
* @return {@code LongSum} instance.
*/
public static LongSum of(long... values) {
final Int128 s = Int128.create();
for (final long x : values) {
s.add(x);
}
return new LongSum(s);
}
/**
* Returns an instance populated using the specified range of {@code values}.
*
* <p>When the range is empty, the result is zero.
*
* @param values Values.
* @param from Inclusive start of the range.
* @param to Exclusive end of the range.
* @return {@code LongSum} instance.
* @throws IndexOutOfBoundsException if the sub-range is out of bounds
* @since 1.2
*/
public static LongSum ofRange(long[] values, int from, int to) {
Statistics.checkFromToIndex(from, to, values.length);
return createFromRange(values, from, to);
}
/**
* Create an instance using the specified range of {@code values}.
*
* <p>Warning: No range checks are performed.
*
* @param values Values.
* @param from Inclusive start of the range.
* @param to Exclusive end of the range.
* @return {@code LongSum} instance.
*/
static LongSum createFromRange(long[] values, int from, int to) {
final Int128 s = Int128.create();
for (int i = from; i < to; i++) {
s.add(values[i]);
}
return new LongSum(s);
}
/**
* Gets the sum.
*
* <p>This is package private for use in {@link LongStatistics}.
*
* @return the sum
*/
Int128 getSum() {
return sum;
}
/**
* Updates the state of the statistic to reflect the addition of {@code value}.
*
* @param value Value.
*/
@Override
public void accept(long value) {
sum.add(value);
}
/**
* Gets the sum of all input values.
*
* <p>When no values have been added, the result is zero.
*
* <p>Warning: This will raise an {@link ArithmeticException}
* if the result is not within the range {@code [-2^31, 2^31)}.
*
* @return sum of all values.
* @throws ArithmeticException if the {@code result} overflows an {@code int}
* @see #getAsBigInteger()
*/
@Override
public int getAsInt() {
return sum.toIntExact();
}
/**
* Gets the sum of all input values.
*
* <p>When no values have been added, the result is zero.
*
* <p>Warning: This will raise an {@link ArithmeticException}
* if the result is not within the range {@code [-2^63, 2^63)}.
*
* @return sum of all values.
* @throws ArithmeticException if the {@code result} overflows a {@code long}
* @see #getAsBigInteger()
*/
@Override
public long getAsLong() {
return sum.toLongExact();
}
/**
* Gets the sum of all input values.
*
* <p>When no values have been added, the result is zero.
*
* <p>Note that this conversion can lose information about the precision of the
* {@code BigInteger} value.
*
* @return sum of all values.
* @see #getAsBigInteger()
*/
@Override
public double getAsDouble() {
return sum.toDouble();
}
/**
* Gets the sum of all input values.
*
* <p>When no values have been added, the result is zero.
*
* @return sum of all values.
*/
@Override
public BigInteger getAsBigInteger() {
return sum.toBigInteger();
}
@Override
public LongSum combine(LongSum other) {
sum.add(other.sum);
return this;
}
}