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	/*
	* Copyright (c) 2012, 2017, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/
	package java.util;

	import java.util.function.DoubleConsumer;
	import java.util.stream.Collector;
	import java.util.stream.DoubleStream;

	/**
	* A state object for collecting statistics such as count, min, max, sum, and
	* average.
	*
	* <p>This class is designed to work with (though does not require)
	* {@linkplain java.util.stream streams}. For example, you can compute
	* summary statistics on a stream of doubles with:
	* <pre> {@code
	* DoubleSummaryStatistics stats = doubleStream.collect(DoubleSummaryStatistics::new,
	* DoubleSummaryStatistics::accept,
	* DoubleSummaryStatistics::combine);
	* }</pre>
	*
	* <p>{@code DoubleSummaryStatistics} can be used as a
	* {@linkplain java.util.stream.Stream#collect(Collector) reduction}
	* target for a {@linkplain java.util.stream.Stream stream}. For example:
	*
	* <pre> {@code
	* DoubleSummaryStatistics stats = people.stream()
	* .collect(Collectors.summarizingDouble(Person::getWeight));
	*}</pre>
	*
	* This computes, in a single pass, the count of people, as well as the minimum,
	* maximum, sum, and average of their weights.
	*
	* @implNote This implementation is not thread safe. However, it is safe to use
	* {@link java.util.stream.Collectors#summarizingDouble(java.util.function.ToDoubleFunction)
	* Collectors.summarizingDouble()} 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 1.8
	*/
	public class DoubleSummaryStatistics implements DoubleConsumer {
	private long count;
	private double sum;
	private double sumCompensation; // Low order bits of sum
	private double simpleSum; // Used to compute right sum for non-finite inputs
	private double min = Double.POSITIVE_INFINITY;
	private double max = Double.NEGATIVE_INFINITY;

	/**
	* Constructs an empty instance with zero count, zero sum,
	* {@code Double.POSITIVE_INFINITY} min, {@code Double.NEGATIVE_INFINITY}
	* max and zero average.
	*/
	public DoubleSummaryStatistics() { }

	/**
	* Constructs a non-empty instance with the specified {@code count},
	* {@code min}, {@code max}, and {@code sum}.
	*
	* <p>If {@code count} is zero then the remaining arguments are ignored and
	* an empty instance is constructed.
	*
	* <p>If the arguments are inconsistent then an {@code IllegalArgumentException}
	* is thrown. The necessary consistent argument conditions are:
	* <ul>
	* <li>{@code count >= 0}</li>
	* <li>{@code (min <= max && !isNaN(sum)) \|\| (isNaN(min) && isNaN(max) && isNaN(sum))}</li>
	* </ul>
	* @apiNote
	* The enforcement of argument correctness means that the retrieved set of
	* recorded values obtained from a {@code DoubleSummaryStatistics} source
	* instance may not be a legal set of arguments for this constructor due to
	* arithmetic overflow of the source's recorded count of values.
	* The consistent argument conditions are not sufficient to prevent the
	* creation of an internally inconsistent instance. An example of such a
	* state would be an instance with: {@code count} = 2, {@code min} = 1,
	* {@code max} = 2, and {@code sum} = 0.
	*
	* @param count the count of values
	* @param min the minimum value
	* @param max the maximum value
	* @param sum the sum of all values
	* @throws IllegalArgumentException if the arguments are inconsistent
	* @since 10
	*/
	public DoubleSummaryStatistics(long count, double min, double max, double sum)
	throws IllegalArgumentException {
	if (count < 0L) {
	throw new IllegalArgumentException("Negative count value");
	} else if (count > 0L) {
	if (min > max)
	throw new IllegalArgumentException("Minimum greater than maximum");

	// All NaN or non NaN
	var ncount = DoubleStream.of(min, max, sum).filter(Double::isNaN).count();
	if (ncount > 0 && ncount < 3)
	throw new IllegalArgumentException("Some, not all, of the minimum, maximum, or sum is NaN");

	this.count = count;
	this.sum = sum;
	this.simpleSum = sum;
	this.sumCompensation = 0.0d;
	this.min = min;
	this.max = max;
	}
	// Use default field values if count == 0
	}

	/**
	* Records another value into the summary information.
	*
	* @param value the input value
	*/
	@Override
	public void accept(double value) {
	++count;
	simpleSum += value;
	sumWithCompensation(value);
	min = Math.min(min, value);
	max = Math.max(max, value);
	}

	/**
	* Combines the state of another {@code DoubleSummaryStatistics} into this
	* one.
	*
	* @param other another {@code DoubleSummaryStatistics}
	* @throws NullPointerException if {@code other} is null
	*/
	public void combine(DoubleSummaryStatistics other) {
	count += other.count;
	simpleSum += other.simpleSum;
	sumWithCompensation(other.sum);
	sumWithCompensation(other.sumCompensation);
	min = Math.min(min, other.min);
	max = Math.max(max, other.max);
	}

	/**
	* Incorporate a new double value using Kahan summation /
	* compensated summation.
	*/
	private void sumWithCompensation(double value) {
	double tmp = value - sumCompensation;
	double velvel = sum + tmp; // Little wolf of rounding error
	sumCompensation = (velvel - sum) - tmp;
	sum = velvel;
	}

	/**
	* Return the count of values recorded.
	*
	* @return the count of values
	*/
	public final long getCount() {
	return count;
	}

	/**
	* Returns the sum of values recorded, or zero if no values have been
	* recorded.
	*
	* <p> The value of a floating-point sum is a function both of the
	* input values as well as the order of addition operations. The
	* order of addition operations of this method is intentionally
	* not defined to allow for implementation flexibility to improve
	* the speed and accuracy of the computed result.
	*
	* In particular, this method may be implemented using compensated
	* summation or other technique to reduce the error bound in the
	* numerical sum compared to a simple summation of {@code double}
	* values.
	*
	* Because of the unspecified order of operations and the
	* possibility of using differing summation schemes, the output of
	* this method may vary on the same input values.
	*
	* <p>Various conditions can result in a non-finite sum being
	* computed. This can occur even if the all the recorded values
	* being summed are finite. If any recorded value is non-finite,
	* the sum will be non-finite:
	*
	* <ul>
	*
	* <li>If any recorded value is a NaN, then the final sum will be
	* NaN.
	*
	* <li>If the recorded values contain one or more infinities, the
	* sum will be infinite or NaN.
	*
	* <ul>
	*
	* <li>If the recorded values contain infinities of opposite sign,
	* the sum will be NaN.
	*
	* <li>If the recorded values contain infinities of one sign and
	* an intermediate sum overflows to an infinity of the opposite
	* sign, the sum may be NaN.
	*
	* </ul>
	*
	* </ul>
	*
	* It is possible for intermediate sums of finite values to
	* overflow into opposite-signed infinities; if that occurs, the
	* final sum will be NaN even if the recorded values are all
	* finite.
	*
	* If all the recorded values are zero, the sign of zero is
	* <em>not</em> guaranteed to be preserved in the final sum.
	*
	* @apiNote Values sorted by increasing absolute magnitude tend to yield
	* more accurate results.
	*
	* @return the sum of values, or zero if none
	*/
	public final double getSum() {
	// Better error bounds to add both terms as the final sum
	double tmp = sum + sumCompensation;
	if (Double.isNaN(tmp) && Double.isInfinite(simpleSum))
	// If the compensated sum is spuriously NaN from
	// accumulating one or more same-signed infinite values,
	// return the correctly-signed infinity stored in
	// simpleSum.
	return simpleSum;
	else
	return tmp;
	}

	/**
	* Returns the minimum recorded value, {@code Double.NaN} if any recorded
	* value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
	* recorded. Unlike the numerical comparison operators, this method
	* considers negative zero to be strictly smaller than positive zero.
	*
	* @return the minimum recorded value, {@code Double.NaN} if any recorded
	* value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
	* recorded
	*/
	public final double getMin() {
	return min;
	}

	/**
	* Returns the maximum recorded value, {@code Double.NaN} if any recorded
	* value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
	* recorded. Unlike the numerical comparison operators, this method
	* considers negative zero to be strictly smaller than positive zero.
	*
	* @return the maximum recorded value, {@code Double.NaN} if any recorded
	* value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
	* recorded
	*/
	public final double getMax() {
	return max;
	}

	/**
	* Returns the arithmetic mean of values recorded, or zero if no
	* values have been recorded.
	*
	* <p> The computed average can vary numerically and have the
	* special case behavior as computing the sum; see {@link #getSum}
	* for details.
	*
	* @apiNote Values sorted by increasing absolute magnitude tend to yield
	* more accurate results.
	*
	* @return the arithmetic mean of values, or zero if none
	*/
	public final double getAverage() {
	return getCount() > 0 ? getSum() / getCount() : 0.0d;
	}

	/**
	* Returns a non-empty string representation of this object suitable for
	* debugging. The exact presentation format is unspecified and may vary
	* between implementations and versions.
	*/
	@Override
	public String toString() {
	return String.format(
	"%s{count=%d, sum=%f, min=%f, average=%f, max=%f}",
	this.getClass().getSimpleName(),
	getCount(),
	getSum(),
	getMin(),
	getAverage(),
	getMax());
	}
	}

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