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Implementation of linear-chain Conditional Random Fields (CRF) in pure Java

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package com.asher_stern.crf.utilities;

import java.math.BigDecimal;
import java.math.MathContext;

import org.apache.log4j.Logger;

/**
 * 
 *
 * 
 * Date: Oct 15, 2016
 * @author Asher Stern
 *
 */
public class ArithmeticUtilities
{
	public static final MathContext MC = MathContext.DECIMAL128;
	
	public static final BigDecimal DOUBLE_MAX = big(Double.MAX_VALUE);
	
	public static final BigDecimal BIG_DECIMAL_E = big(Math.E);
	public static final BigDecimal BIG_DECIMAL_TWO = new BigDecimal("2.0", MC);
	public static final BigDecimal BIG_DECIMAL_E_TO_512 = BIG_DECIMAL_E.pow(512);
	public static final BigDecimal BIG_DECIMAL_512 = new BigDecimal("512", MC);
	public static final BigDecimal BIG_DECIMAL_LOG_DOUBLE_MAX = big(Math.log(Double.MAX_VALUE));
	
	public static BigDecimal big(double d)
	{
		return new BigDecimal(d, MC);
	}
	

	public static BigDecimal log(BigDecimal d)
	{
		// long debug_counter = 0;
		BigDecimal ret = BigDecimal.ZERO;
		while (d.compareTo(DOUBLE_MAX)>0)
		{
			ret = safeAdd(ret, BIG_DECIMAL_512);
			d = safeDivide(d, BIG_DECIMAL_E_TO_512);
			if (d.compareTo(BigDecimal.ONE)<0) {throw new CrfException("Anomaly");}
			// ++debug_counter;
		}
		ret = safeAdd(ret, big(Math.log(d.doubleValue())));
		// if ( logger.isDebugEnabled() && (debug_counter>0) ) {logger.debug("log() performed "+debug_counter+" iterations.");}
		return ret;
	}
	
	
	public static BigDecimal exp(BigDecimal d)
	{
		if (d.compareTo(BIG_DECIMAL_LOG_DOUBLE_MAX)<=0)
		{
			return big(Math.exp(d.doubleValue()));
		}
		else
		{
			BigDecimal half = safeDivide(d, BIG_DECIMAL_TWO);
			BigDecimal halfExp = exp(half);
			return safeMultiply(halfExp, halfExp);
		}
	}
	
	public static BigDecimal safeAdd(final BigDecimal d1, final BigDecimal d2)
	{
		return d1.add(d2, MC);
	}
	
	public static BigDecimal safeSubtract(final BigDecimal d1, final BigDecimal d2)
	{
		return d1.subtract(d2, MC);
	}
	
	public static BigDecimal safeMultiply(final BigDecimal d1, final BigDecimal d2)
	{
		return d1.multiply(d2, MC);
	}
	
	public static BigDecimal safeMultiply(final BigDecimal d1, final BigDecimal d2, BigDecimal...ds)
	{
		BigDecimal ret = safeMultiply(d1, d2);
		for (BigDecimal d : ds)
		{
			ret = safeMultiply(ret, d);
		}
		return ret;
	}
	
	public static BigDecimal safeDivide(final BigDecimal d1, final BigDecimal d2)
	{
		return d1.divide(d2, MC);
	}
	
	@SuppressWarnings("unused")
	private static final Logger logger = Logger.getLogger(ArithmeticUtilities.class);
}