log BigDecimal - Java java.math

Java examples for java.math:BigDecimal Calculation

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Description

log BigDecimal

Demo Code


//package com.java2s;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.math.MathContext;
import java.math.RoundingMode;

public class Main {
    public static void main(String[] argv) throws Exception {
        int base_int = 2;
        BigDecimal x = new BigDecimal("1234");
        System.out.println(log(base_int, x));
    }/*from  ww  w  .  java  2s.  c o  m*/

    /**
     * @see http://stackoverflow.com/questions/739532/logarithm-of-a-bigdecimal for 
     * reference.
     * 
     * @param base_int
     * @param x
     * @return
     */
    public static BigDecimal log(int base_int, BigDecimal x) {
        BigDecimal result = BigDecimal.ZERO;

        BigDecimal input = new BigDecimal(x.toString());
        int decimalPlaces = 100;
        int scale = input.precision() + decimalPlaces;

        int maxite = 10000;
        int ite = 0;
        BigDecimal maxError_BigDecimal = new BigDecimal(BigInteger.ONE,
                decimalPlaces + 1);
        // System.out.println("maxError_BigDecimal " + maxError_BigDecimal);
        // System.out.println("scale " + scale);

        RoundingMode a_RoundingMode = RoundingMode.UP;

        BigDecimal two_BigDecimal = new BigDecimal("2");
        BigDecimal base_BigDecimal = new BigDecimal(base_int);

        while (input.compareTo(base_BigDecimal) == 1) {
            result = result.add(BigDecimal.ONE);
            input = input.divide(base_BigDecimal, scale, a_RoundingMode);
        }

        BigDecimal fraction = new BigDecimal("0.5");
        input = input.multiply(input);
        BigDecimal resultplusfraction = result.add(fraction);
        while (((resultplusfraction).compareTo(result) == 1)
                && (input.compareTo(BigDecimal.ONE) == 1)) {
            if (input.compareTo(base_BigDecimal) == 1) {
                input = input
                        .divide(base_BigDecimal, scale, a_RoundingMode);
                result = result.add(fraction);
            }
            input = input.multiply(input);
            fraction = fraction.divide(two_BigDecimal, scale,
                    a_RoundingMode);
            resultplusfraction = result.add(fraction);
            if (fraction.abs().compareTo(maxError_BigDecimal) == -1) {
                break;
            }
            if (maxite == ite) {
                break;
            }
            ite++;
        }

        MathContext a_MathContext = new MathContext(
                ((decimalPlaces - 1) + (result.precision() - result.scale())),
                RoundingMode.HALF_UP);
        BigDecimal roundedResult = result.round(a_MathContext);
        BigDecimal strippedRoundedResult = roundedResult
                .stripTrailingZeros();
        //return result;
        //return result.round(a_MathContext);
        return strippedRoundedResult;
    }
}

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