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jBasics is a collection of useful utility classes for Java. This includes helper for XML, mathematic functions, restful web services helper, pattern oriented programming interfaces and more. Currently Java7 and up is supported. Version 1.0 will required at leaset Java8.
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/*
 * Copyright (c) 2009-2015
 * 	IT-Consulting Stephan Schloepke (http://www.schloepke.de/)
 * 	klemm software consulting Mirko Klemm (http://www.klemm-scs.com/)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.jbasics.math.impl;

import org.jbasics.checker.ContractCheck;
import org.jbasics.math.AlgorithmStrategy;
import org.jbasics.math.IrationalNumber;
import org.jbasics.math.MemorizedIrationalNumber;

import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
import java.util.concurrent.atomic.AtomicMarkableReference;

/**
 * Implements the {@link IrationalNumber} and memorizes the most precise result.
 *
 * @author Stephan Schloepke
 * @since 1.0
 */
public class BigDecimalIrationalNumber implements MemorizedIrationalNumber {
	private final AlgorithmStrategy algorithm;
	/**
	 * Holds the input value x which is a immutable constant.
	 */
	private final BigDecimal[] xn;
	/**
	 * Holds the calculated memorized value with the mark indicating if the value is a final exakt result.
	 */
	private final AtomicMarkableReference value;

	/**
	 * Create an {@link BigDecimalIrationalNumber} with the given x as input and no initial value. The first calculation
	 * will be delayed until the value is accessed with {@link IrationalNumber#valueToPrecision(MathContext)}.
	 *
	 * @param xn The input value of the algorithm (if the algorithm requires more input values these needs to be stored
	 *          separately. Be aware that while this implementation memorized the result thread safe any other
	 *          calculation value might not be thread safe. So all input variables should be considered constant like
	 *          the x value is).
	 *
	 * @since 1.0
	 */
	protected BigDecimalIrationalNumber(AlgorithmStrategy algorithm, BigDecimal... xn) {
		this(null, algorithm, xn);
	}

	/**
	 * Create an {@link BigDecimalIrationalNumber} with the given x as input and the optional initial value as initial
	 * value of the calculation.
	 *
	 * @param xn       The input value of the algorithm (if the algorithm requires more input values these needs to be
	 *                stored separately. Be aware that while this implementation memorized the result thread safe any
	 *                other calculation value might not be thread safe. So all input variables should be considered
	 *                constant like the x value is).
	 * @param initial The initial value to use.
	 *
	 * @since 1.0
	 */
	protected BigDecimalIrationalNumber(BigDecimal initial, AlgorithmStrategy algorithm, BigDecimal... xn) {
		this.algorithm = ContractCheck.mustNotBeNull(algorithm, "algorithm");
		this.xn = ContractCheck.mustNotBeNull(xn, "xn");
		this.value = new AtomicMarkableReference(initial, false);
	}

	/*
	 * (non-Javadoc)
	 * @see org.jbasics.math.IrationalNumber#valueToPrecision(java.math.MathContext)
	 */
	public BigDecimal valueToPrecision(MathContext mc) {
		boolean[] mark = new boolean[1];
		BigDecimal result = this.value.get(mark);
		if (!mark[0]) {
			if (result == null || result.precision() <= mc.getPrecision()) {
				MathContext extendedMC = new MathContext(mc.getPrecision() + 5, RoundingMode.FLOOR);
				BigDecimal morePrecise = this.algorithm.calculate(extendedMC, result, this.xn);
				if (!this.value.compareAndSet(result, morePrecise, mark[0], morePrecise.precision() < mc.getPrecision())) {
					result = this.value.get(mark);
					if (!mark[0] && (result == null || result.precision() < morePrecise.precision())) {
						this.value.compareAndSet(result, morePrecise, mark[0], morePrecise.precision() < mc.getPrecision());
						result = morePrecise;
					}
				} else {
					result = morePrecise;
				}
			}
		}
		return result.round(mc);
	}

	/*
	 * (non-Javadoc)
	 * @see org.jbasics.math.MemorizedIrationalNumber#precision()
	 */
	public int precision() {
		BigDecimal t = this.value.getReference();
		return t == null ? 0 : t.precision();
	}

	/*
	 * (non-Javadoc)
	 * @see org.jbasics.math.MemorizedIrationalNumber#isExact()
	 */
	public boolean isExact() {
		return this.value.isMarked();
	}
}