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 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.
* */
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 'x'. 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's actually floor log2)
v = x;
y = - 1;
while (v > 0)
{
v >>= 1;
y++;
}
return y;
}
}
}
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