//******************************************************************************
//
// File:    Mathe.java
// Package: edu.rit.util
// Unit:    Class edu.rit.util.Mathe
//
// This Java source file is copyright (C) 2010 by Alan Kaminsky. All rights
// reserved. For further information, contact the author, Alan Kaminsky, at
// ark@cs.rit.edu.
//
// This Java source file is part of the Parallel Java Library ("PJ"). PJ is free
// software; you can redistribute it and/or modify it under the terms of the GNU
// General Public License as published by the Free Software Foundation; either
// version 3 of the License, or (at your option) any later version.
//
// PJ is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE. See the GNU General Public License for more details.
//
// A copy of the GNU General Public License is provided in the file gpl.txt. You
// may also obtain a copy of the GNU General Public License on the World Wide
// Web at http://www.gnu.org/licenses/gpl.html.
//
//******************************************************************************

package edu.rit.util;

/**
 * Class Mathe provides useful mathematical operations. The class is named
 * "Mathe" so the compiler won't confuse it with class java.lang.Math.
 *
 * @author  Alan Kaminsky
 * @version 11-Feb-2010
 */
public class Mathe
	{

// Prevent construction.

	private Mathe()
		{
		}

// Exported operations.

	/**
	 * Compute the integer square root of the integer x. The value
	 * floor(x1/2) is returned. The answer is calculated
	 * using an exact integer algorithm taken from:
	 * 

	 * 

	 * J. Crenshaw. Integer square roots.
	 * http://www.embedded.com/98/9802fe2.htm
	 * 
	 *
	 * @param  x  Input.
	 *
	 * @return  Floor(x1/2).
	 *
	 * @exception  ArithmeticException
	 *     (unchecked exception) Thrown if x < 0.
	 */
	public static int sqrt
		(int x)
		{
		if (x < 0)
			{
			throw new ArithmeticException ("Mathe.sqrt(): x < 0");
			}
		int rem = 0;
		int root = 0;
		for (int i = 0; i < 16; ++ i)
			{
			root <<= 1;
			rem = (rem << 2) | (x >>> 30);
			x <<= 2;
			++ root;
			if (root <= rem)
				{
				rem -= root;
				++ root;
				}
			else
				{
				-- root;
				}
			}
		return root >>> 1;
		}

// Unit test main program.

//	/**
//	 * Unit test main program.
//	 */
//	public static void main
//		(String[] args)
//		{
//		for (int x = 0; x <= 100000000; ++ x)
//			{
//			if ((x % 10000000) == 0) System.out.printf ("%d%n", x);
//			int y = Mathe.sqrt(x);
//			if (y*y > x || x >= (y + 1)*(y + 1))
//				{
//				System.out.printf ("x = %d, sqrt(x) = %d, fail%n", x, y);
//				}
//			}
//		}

	}