Calculates the floor of the log, base 2, of 'x'.

   
 
    
/*
* CVS identifier:
*
* $Id: MathUtil.java,v 1.15 2001/09/14 08:48:51 grosbois Exp $
*
* Class:                   MathUtil
*
* Description:             Utility mathematical methods
*
*
*
* COPYRIGHT:
* 
* This software module was originally developed by Raphaël Grosbois and
* Diego Santa Cruz (Swiss Federal Institute of Technology-EPFL); Joel
* Askelöf (Ericsson Radio Systems AB); and Bertrand Berthelot, David
* Bouchard, Félix 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.
* */
using System;
namespace CSJ2K.j2k.util
{
  
  /// <summary> This class contains a collection of utility methods fro mathematical
  /// operations. All methods are static.
  /// 
  /// </summary>
  public class MathUtil
  {

    /// <summary> Method that calculates the floor of the log, base 2, of &#039;x&#039;. The
    /// calculation is performed in integer arithmetic, therefore, it is exact.
    /// 
    /// </summary>
    /// <param name="x">The value to calculate log2 on.
    /// 
    /// </param>
    /// <returns> floor(log(x)/log(2)), calculated in an exact way.
    /// 
    /// </returns>
    public static int log2(int x)
    {
      int y, v;
      // No log of 0 or negative
      if (x <= 0)
      {
        throw new System.ArgumentException("" + x + " <= 0");
      }
      // Calculate log2 (it&#039;s actually floor log2)
      v = x;
      y = - 1;
      while (v > 0)
      {
        v >>= 1;
        y++;
      }
      return y;
    }
     }
}