Calculate the floor of the log, base 2 : Math Functions « Development « Java Tutorial

 * $RCSfile:,v $
 * $Revision: 1.1 $
 * $Date: 2005/02/11 05:02:25 $
 * $State: Exp $
 * Class:                   MathUtil
 * Description:             Utility mathematical methods
 * This software module was originally developed by Raphal Grosbois and
 * Diego Santa Cruz (Swiss Federal Institute of Technology-EPFL); Joel
 * Askelf (Ericsson Radio Systems AB); and Bertrand Berthelot, David
 * Bouchard, Flix Henry, Gerard Mozelle and Patrice Onno (Canon Research
 * Centre France S.A) in the course of development of the JPEG2000
 * standard as specified by ISO/IEC 15444 (JPEG 2000 Standard). This
 * software module is an implementation of a part of the JPEG 2000
 * Standard. Swiss Federal Institute of Technology-EPFL, Ericsson Radio
 * Systems AB and Canon Research Centre France S.A (collectively JJ2000
 * Partners) agree not to assert against ISO/IEC and users of the JPEG
 * 2000 Standard (Users) any of their rights under the copyright, not
 * including other intellectual property rights, for this software module
 * with respect to the usage by ISO/IEC and Users of this software module
 * or modifications thereof for use in hardware or software products
 * claiming conformance to the JPEG 2000 Standard. Those intending to use
 * this software module in hardware or software products are advised that
 * their use may infringe existing patents. The original developers of
 * this software module, JJ2000 Partners and ISO/IEC assume no liability
 * for use of this software module or modifications thereof. No license
 * or right to this software module is granted for non JPEG 2000 Standard
 * conforming products. JJ2000 Partners have full right to use this
 * software module for his/her own purpose, assign or donate this
 * software module to any third party and to inhibit third parties from
 * using this software module for non JPEG 2000 Standard conforming
 * products. This copyright notice must be included in all copies or
 * derivative works of this software module.
 * Copyright (c) 1999/2000 JJ2000 Partners.
 * */

 * This class contains a collection of utility methods fro mathematical
 * operations. All methods are static.
 * */
public class MathUtil {

     * Method that calculates the floor of the log, base 2,
     * of 'x'. The calculation is performed in integer arithmetic,
     * therefore, it is exact.
     * @param x The value to calculate log2 on.
     * @return floor(log(x)/log(2)), calculated in an exact way.
     * */
    public static int log2(int x) {
        int y,v;
        // No log of 0 or negative
        if (x <= 0) {
            throw new IllegalArgumentException(""+x+" <= 0");
        // Calculate log2 (it's actually floor log2)
        v = x;
        y = -1;
        while (v>0) {
            v >>=1;
        return y;


6.17.Math Functions
6.17.1.Math Class Methods
6.17.2.Use math functions
6.17.3.Testing the Math class methods
6.17.4.Floating Point Number Enhancements in JDK 6
6.17.10.Demonstrate toDegrees() and toRadians().
6.17.11.Find absolute value of float, int, double and long using Math.abs
6.17.12.Find ceiling value of a number using Math.ceil
6.17.13.Find exponential value of a number using Math.exp
6.17.14.Find floor value of a number using Math.floor
6.17.15.Find maximum of two numbers using Math.max
6.17.16.Find natural logarithm value of a number using Math.log
6.17.17.Find power using Math.pow
6.17.18.Find square root of a number using Math.sqrt
6.17.19.Round Java float and double numbers using Math.round
6.17.21.Normalizes an angle to a relative angle.
6.17.22.Normalizes an angle to an absolute angle.
6.17.23.Normalizes an angle to be near an absolute angle
6.17.24.Calculate the floor of the log, base 2
6.17.25.Greatest Common Divisor (GCD) of positive integer numbers
6.17.26.Least Common Multiple (LCM) of two strictly positive integer numbers
6.17.27.Moving Average
6.17.28.Normalize an angle in a 2&pi wide interval around a center value.
6.17.29.Returns n!. Shorthand for n Factorial, the product of the numbers 1,...,n as a double.
6.17.30.Returns n!. Shorthand for n Factorial, the product of the numbers 1,...,n.
6.17.31.Returns the hyperbolic cosine of x.
6.17.32.Returns the hyperbolic sine of x.
6.17.33.Returns the natural log of the ( Binomial Coefficient
6.17.34.Returns the natural logarithm of n!.
6.17.35.Round the given value to the specified number of decimal places. The value is rounded using the BigDecimal.ROUND_HALF_UP method.
6.17.36.Value is rounded using the given method which is any method defined in BigDecimal
6.17.37.sqrt(a^2 + b^2) without under/overflow