LogarithmAlgorithmStrategy.java

/*
 * 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.strategies;

import org.jbasics.math.AlgorithmStrategy;

import java.math.BigDecimal;
import java.math.MathContext;
import java.util.concurrent.atomic.AtomicReferenceArray;

public class LogarithmAlgorithmStrategy implements AlgorithmStrategy<BigDecimal> {
	private final AlgorithmStrategy<BigDecimal> naturalLogrithm;

	private final AtomicReferenceArray<BigDecimal> baseCache = new AtomicReferenceArray<BigDecimal>(15);

	public LogarithmAlgorithmStrategy() {
		this(null);
	}

	public LogarithmAlgorithmStrategy(final AlgorithmStrategy<BigDecimal> naturalLogarithm) {
		this.naturalLogrithm = naturalLogarithm != null ? naturalLogarithm : new NaturalLogarithmAlgorithmStrategy();
	}

	public BigDecimal calculate(final MathContext mc, final BigDecimal guess, final BigDecimal... xn) {
		if (xn == null || xn.length != 2) {
			throw new IllegalArgumentException("Illegal amount of arguments supplied (required 2, got " + (xn == null ? 0 : xn.length) + ")"); //$NON-NLS-1$ //$NON-NLS-2$
		}
		BigDecimal x = xn[0];
		BigDecimal base = xn[1];
		return this.naturalLogrithm.calculate(mc, null, x).divide(calculateBase(mc, base), mc);
	}

	private BigDecimal calculateBase(final MathContext mc, final BigDecimal base) {
		try {
			int temp = base.intValueExact() - 2;
			if (temp >= 0 && temp < this.baseCache.length()) {
				return getOrCreateCached(mc, base, temp);
			}
		} catch (ArithmeticException e) {
			// We do nothing but directly calculate the result
		}
		return this.naturalLogrithm.calculate(mc, null, base);
	}

	private BigDecimal getOrCreateCached(final MathContext mc, final BigDecimal base, int baseIndex) {
		BigDecimal result = this.baseCache.get(baseIndex);
		if (result == null || result.precision() <= mc.getPrecision()) {
			BigDecimal newResult = this.naturalLogrithm.calculate(mc, result, base);
			if (!this.baseCache.compareAndSet(baseIndex, result, newResult)) {
				// here we know that we could not update the value so lets check the
				// precision
				result = this.baseCache.get(baseIndex);
				if (result == null || result.precision() < newResult.precision()) {
					this.baseCache.set(baseIndex, newResult);
				} else {
					return result;
				}
			}
			return newResult;
		}
		return result;
	}
}