Get log base 2 of a double. - Java java.lang

Java examples for java.lang:Math Operation

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Description

Get log base 2 of a double.

Demo Code

/**   Basic numeric operations not included in standard Java run-time library.
 *
 *   <p>/*from w ww  .j  ava2 s. co  m*/
 *   The binomial methods are modified from those in the Colt library.
 *   </p>
 *
 *   <p>
 *   The following methods for trigonometric functions come from the
 *   Sfun class written by Visual Numerics.
 *   </p>
 *
 *   <ul>
 *   <li>acosh</li>
 *   <li>asinh</li>
 *   <li>atanh</li>
 *   <li>cot</li>
 *   <li>cosh</li>
 *   <li>sinh</li>
 *   <li>tanh</li>
 *   </ul>
 *
 *   <p>
 *   These methods are covered by the following license.
 *   </p>
 *
 * -------------------------------------------------------------------------
 *   $Id: Sfun.java,v 1.1.1.1 1999/03/05 21:43:39 brophy Exp $
 * -------------------------------------------------------------------------
 * Copyright (c) 1997 - 1998 by Visual Numerics, Inc. All rights reserved.
 *
 * Permission to use, copy, modify, and distribute this software is freely
 * granted by Visual Numerics, Inc., provided that the copyright notice
 * above and the following warranty disclaimer are preserved in human
 * readable form.
 *
 * Because this software is licensed free of charge, it is provided
 * "AS IS", with NO WARRANTY.  TO THE EXTENT PERMITTED BY LAW, VNI
 * DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
 * TO ITS PERFORMANCE, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
 * VNI WILL NOT BE LIABLE FOR ANY DAMAGES WHATSOEVER ARISING OUT OF THE USE
 * OF OR INABILITY TO USE THIS SOFTWARE, INCLUDING BUT NOT LIMITED TO DIRECT,
 * INDIRECT, SPECIAL, CONSEQUENTIAL, PUNITIVE, AND EXEMPLARY DAMAGES, EVEN
 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * -------------------------------------------------------------------------
 */

public class Main{
    public static void main(String[] argv) throws Exception{
        double x = 2.45678;
        System.out.println(log2(x));
    }
    /**   Get log base 2 of a double.
     *
     *   @param   x   The number whose log base 2 value is desired.
     *
     *   @return      The log base 2 of x.
     *            If x is <= 0, 0 is returned.
     *
     *   <p>
     *   Example:   log2( 32 ) is 5.0D .
     *   </p>
     */

    public static double log2(double x) {
        double result = 0.0D;

        if (x > 0.0D) {
            result = safeLog(x) * Constants.LN2INV;
        }

        return result;
    }
    /**   Return natural log of a double.
     *
     *   @param   x   The number whose natural log is desired.
     *
     *   @return      The natural log of x.  If x is zero,
     *            returns 0.
     */

    public static double safeLog(double x) {
        if (x == 0.0D) {
            return 0.0D;
        } else {
            return Math.log(x);
        }
    }
}

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