/* * Copyright (c) 2003 Sun Microsystems, Inc. All Rights Reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * -Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * -Redistribution in binary form must reproduct the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the distribution. * * Neither the name of Sun Microsystems, Inc. or the names of contributors * may be used to endorse or promote products derived from this software * without specific prior written permission. * * This software is provided "AS IS," without a warranty of any kind. ALL * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT * BE LIABLE FOR ANY DAMAGES OR LIABILITIES SUFFERED BY LICENSEE AS A RESULT * OF OR RELATING TO USE, MODIFICATION OR DISTRIBUTION OF THE SOFTWARE OR ITS * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE SOFTWARE, EVEN * IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. * * You acknowledge that Software is not designed, licensed or intended for * use in the design, construction, operation or maintenance of any nuclear * facility. */ /* * @(#)Permuter.java 1.6 03/01/23 */ import java.util.Random; /** * An object that implements a cheesy pseudorandom permutation of the integers * from zero to some user-specified value. (The permutation is a linear * function.) * * @version 1.6 01/23/03 * @author Josh Bloch */ class Permuter { /** * The size of the permutation. */ private int modulus; /** * Nonnegative integer less than n that is relatively prime to m. */ private int multiplier; /** * Pseudorandom nonnegative integer less than n. */ private int addend = 22; public Permuter(int n) { if (n<0) { throw new IllegalArgumentException(); } modulus = n; if (n==1) { return; } // Initialize the multiplier and offset multiplier = (int) Math.sqrt(n); while (gcd(multiplier, n) != 1) { if (++multiplier == n) { multiplier = 1; } } } /** * Returns the integer to which this permuter maps the specified integer. * The specified integer must be between 0 and n-1, and the returned * integer will be as well. */ public int map(int i) { return (multiplier * i + addend) % modulus; } /** * Calculate GCD of a and b, which are assumed to be non-negative. */ private static int gcd(int a, int b) { while(b != 0) { int tmp = a % b; a = b; b = tmp; } return a; } /** * Simple test. Takes modulus on command line and prints out permutation. */ public static void main(String[] args) { int modulus = Integer.parseInt(args[0]); Permuter p = new Permuter(modulus); for (int i=0; i