/*
 
* Java GPX Library (@__identifier__@).
 
* Copyright (c) @__year__@ Franz Wilhelmstötter
 
*
 
* 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.
 
*
 
* Author:
 
*
    
Franz Wilhelmstötter (franz.wilhelmstoetter@gmail.com)
 
*/
package io.jenetics.jpx.geom;

import static java.lang.Double.isInfinite;
import static java.lang.Double.isNaN;
import static java.util.Objects.requireNonNull;

/**
 
* This class implements the the
 
* <a href="http://en.wikipedia.org/wiki/Kahan_summation_algorithm">Kahan
 
* summation algorithm</a>, which significantly reduces the numerical error when
 
* adding double values.
 
*
 
* @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
 
* @since 1.0
 
* @version 1.0
 
*/

final class DoubleAdder
	
extends Number
	
implements Comparable<DoubleAdder>
{
	
private static final long serialVersionUID = 1L;

	
private double _sum = 0.0;
	
private double _simpleSum = 0.0;
	
private double _compensation = 0.0;

	
/**
	 
* Create a new adder with the initial value of {@code 0.0}.
	 
*/


	
DoubleAdder() {
	
}

	
/**
	 
* Reset the adder to the initial value of {@code 0.0}.
	 
*
	 
* @return {@code this} adder, for command chaining
	 
*/

	
private DoubleAdder reset() {
		
_sum = 0.0;
		
_simpleSum = 0.0;
		
_compensation = 0.0;
		
return this;
	
}

	
/**
	 
* Set the adder to the given {@code value}.
	 
*
	 
* @param value the new adder value
	 
* @return {@code this} adder, for command chaining
	 
* @throws java.lang.NullPointerException if the given {@code value} is
	 
*
         
{@code null}
	 
*/

	
public DoubleAdder set(final DoubleAdder value) {
		
return reset().add(requireNonNull(value));
	
}

	
/**
	 
* Add the given {@code value} to this adder, using the
	 
* <a href="http://en.wikipedia.org/wiki/Kahan_summation_algorithm">Kahan
	 
* summation algorithm</a>
	 
*
	 
* @param value the {@code value} to add
	 
* @return {@code this} adder, for command chaining
	 
*/

	
public DoubleAdder add(final double value) {
		
addWithCompensation(value);
		
_simpleSum += value;
		
return this;
	
}

	
/**
	 
* Add the given values to this adder.
	 
*
	 
* @param values the values to add.
	 
* @return {@code this} adder, for command chaining
	 
*/

	
public DoubleAdder add(final double[] values) {
		
for (int i = values.length; --i >= 0;) {
			
add(values[i]);
		
}

		
return this;
	
}

	
private void addWithCompensation(final double value) {
		
final double y = value - _compensation;
		
final double t = _sum + y;
		
_compensation = (t - _sum) - y;
		
_sum = t;
	
}

	
/**
	 
* Add the given {@code value} to this adder, using the
	 
* <a href="http://en.wikipedia.org/wiki/Kahan_summation_algorithm">Kahan
	 
* summation algorithm</a>
	 
*
	 
* @param value the {@code value} to add
	 
* @return {@code this} adder, for command chaining
	 
* @throws java.lang.NullPointerException if the given {@code value} is
	 
*
         
{@code null}
	 
*/

	
public DoubleAdder add(final DoubleAdder value) {
		
addWithCompensation(value._sum);
		
addWithCompensation(value._compensation);
		
_simpleSum += value._simpleSum;
		
return this;
	
}

	
/**
	 
* Add the given {@code value} to this adder, using the
	 
* <a href="http://en.wikipedia.org/wiki/Kahan_summation_algorithm">Kahan
	 
* summation algorithm</a>
	 
*
	 
* @param other the {@code value} to add
	 
* @return {@code this} adder, for command chaining
	 
* @throws java.lang.NullPointerException if the given {@code value} is
	 
*
         
{@code null}
	 
*/

	
public DoubleAdder combine(final DoubleAdder other) {
		
return add(other);
	
}

	
public double value() {
		
final double result =
  
_sum + _compensation;
		
return isNaN(result) && isInfinite(_simpleSum) ? _simpleSum : result;
	
}

	
@Override
	
public int intValue() {
		
return (int)value();
	
}

	
@Override
	
public long longValue() {
		
return (long)value();
	
}

	
@Override
	
public float floatValue() {
		
return (float)value();
	
}

	
@Override
	
public double doubleValue() {
		
return value();
	
}

	
@Override
	
public int compareTo(final DoubleAdder other) {
		
return Double.compare(doubleValue(), other.doubleValue());
	
}

	
@Override
	
public int hashCode() {
		
return Double.hashCode(doubleValue());
	
}

	
@Override
	
public boolean equals(final Object obj) {
		
return obj instanceof DoubleAdder &&
			
Double.compare(doubleValue(), ((DoubleAdder)obj).doubleValue()) == 0;
	
}

	
@Override
	
public String toString() {
		
return Double.toString(doubleValue());
	
}


	
/* *************************************************************************
	 
* Some static helper methods.
	 
**************************************************************************/


	
/**
	 
* Return the sum of the given double array.
	 
*
	 
* @param values the values to sum up.
	 
* @return the sum of the given {@code values}.
	 
* @throws NullPointerException if the given array is {@code null}.
	 
*/

	
public static double sum(final double[] values) {
		
return new DoubleAdder().add(values).doubleValue();
	
}
}