/*
* 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 '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;
		}
		
		/// <summary> Method that calculates the Least Common Multiple (LCM) of two strictly
		/// positive integer numbers.
		/// 
		/// </summary>
		/// <param name="x1">First number
		/// 
		/// </param>
		/// <param name="x2">Second number
		/// 
		/// </param>
		public static int lcm(int x1, int x2)
		{
			if (x1 <= 0 || x2 <= 0)
			{
				throw new System.ArgumentException("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 System.ApplicationException("Cannot find the least common multiple of numbers " + x1 + " and " + x2);
		}
		
		/// <summary> Method that calculates the Least Common Multiple (LCM) of several
		/// positive integer numbers.
		/// 
		/// </summary>
		/// <param name="x">Array containing the numbers.
		/// 
		/// </param>
		public static int lcm(int[] x)
		{
			if (x.Length < 2)
			{
				throw new System.ApplicationException("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 System.ArgumentException("Cannot compute the least " + "common multiple of " + "several numbers where " + "one, at least," + "is negative.");
				}
				tmp = lcm(tmp, x[i]);
			}
			return tmp;
		}
		
		/// <summary> Method that calculates the Greatest Common Divisor (GCD) of two
		/// positive integer numbers.
		/// 
		/// </summary>
		public static int gcd(int x1, int x2)
		{
			if (x1 < 0 || x2 < 0)
			{
				throw new System.ArgumentException("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;
		}
		
		/// <summary> Method that calculates the Greatest Common Divisor (GCD) of several
		/// positive integer numbers.
		/// 
		/// </summary>
		/// <param name="x">Array containing the numbers.
		/// 
		/// </param>
		public static int gcd(int[] x)
		{
			if (x.Length < 2)
			{
				throw new System.ApplicationException("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 System.ArgumentException("Cannot compute the least " + "common multiple of " + "several numbers where " + "one, at least," + "is negative.");
				}
				tmp = gcd(tmp, x[i]);
			}
			return tmp;
		}
	}
}