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/*
* $RCSfile: MathUtil.java,v $
* $Revision: 1.1 $
* $Date: 2005/02/11 05:02:25 $
* $State: 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.
* */
package jj2000.j2k.util;
/**
* 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;
y++;
}
return y;
}
/**
* Method that calculates the Least Common Multiple (LCM) of two strictly
* positive integer numbers.
*
* @param x1 First number
*
* @param x2 Second number
* */
public static final int lcm(int x1,int x2) {
if(x1<=0 || x2<=0) {
throw new IllegalArgumentException("Cannot compute the least "+
"common multiple of two "+
"numbers if one, at least,"+
"is negative.");
}
int max,min;
if (x1>x2) {
max = x1;
min = x2;
} else {
max = x2;
min = x1;
}
for(int i=1; i<=min; i++) {
if( (max*i)%min == 0 ) {
return i*max;
}
}
throw new Error("Cannot find the least common multiple of numbers "+
x1+" and "+x2);
}
/**
* Method that calculates the Least Common Multiple (LCM) of several
* positive integer numbers.
*
* @param x Array containing the numbers.
* */
public static final int lcm(int[] x) {
if(x.length<2) {
throw new Error("Do not use this method if there are less than"+
" two numbers.");
}
int tmp = lcm(x[x.length-1],x[x.length-2]);
for(int i=x.length-3; i>=0; i--) {
if(x[i]<=0) {
throw new IllegalArgumentException("Cannot compute the least "+
"common multiple of "+
"several numbers where "+
"one, at least,"+
"is negative.");
}
tmp = lcm(tmp,x[i]);
}
return tmp;
}
/**
* Method that calculates the Greatest Common Divisor (GCD) of two
* positive integer numbers.
* */
public static final int gcd(int x1,int x2) {
if(x1<0 || x2<0) {
throw new IllegalArgumentException("Cannot compute the GCD "+
"if one integer is negative.");
}
int a,b,g,z;
if(x1>x2) {
a = x1;
b = x2;
} else {
a = x2;
b = x1;
}
if(b==0) return 0;
g = b;
while (g!=0) {
z= a%g;
a = g;
g = z;
}
return a;
}
/**
* Method that calculates the Greatest Common Divisor (GCD) of several
* positive integer numbers.
*
* @param x Array containing the numbers.
* */
public static final int gcd(int[] x) {
if(x.length<2) {
throw new Error("Do not use this method if there are less than"+
" two numbers.");
}
int tmp = gcd(x[x.length-1],x[x.length-2]);
for(int i=x.length-3; i>=0; i--) {
if(x[i]<0) {
throw new IllegalArgumentException("Cannot compute the least "+
"common multiple of "+
"several numbers where "+
"one, at least,"+
"is negative.");
}
tmp = gcd(tmp,x[i]);
}
return tmp;
}
}