| 1 | /* |
| 2 | * Copyright (c) 2003 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * |
| 4 | * Redistribution and use in source and binary forms, with or without |
| 5 | * modification, are permitted provided that the following conditions |
| 6 | * are met: |
| 7 | * |
| 8 | * -Redistributions of source code must retain the above copyright |
| 9 | * notice, this list of conditions and the following disclaimer. |
| 10 | * |
| 11 | * -Redistribution in binary form must reproduct the above copyright |
| 12 | * notice, this list of conditions and the following disclaimer in |
| 13 | * the documentation and/or other materials provided with the distribution. |
| 14 | * |
| 15 | * Neither the name of Sun Microsystems, Inc. or the names of contributors |
| 16 | * may be used to endorse or promote products derived from this software |
| 17 | * without specific prior written permission. |
| 18 | * |
| 19 | * This software is provided "AS IS," without a warranty of any kind. ALL |
| 20 | * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING |
| 21 | * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE |
| 22 | * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN AND ITS LICENSORS SHALL NOT |
| 23 | * BE LIABLE FOR ANY DAMAGES OR LIABILITIES SUFFERED BY LICENSEE AS A RESULT |
| 24 | * OF OR RELATING TO USE, MODIFICATION OR DISTRIBUTION OF THE SOFTWARE OR ITS |
| 25 | * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST |
| 26 | * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, |
| 27 | * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY |
| 28 | * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE SOFTWARE, EVEN |
| 29 | * IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. |
| 30 | * |
| 31 | * You acknowledge that Software is not designed, licensed or intended for |
| 32 | * use in the design, construction, operation or maintenance of any nuclear |
| 33 | * facility. |
| 34 | */ |
| 35 | |
| 36 | /* |
| 37 | * @(#)Permuter.java 1.6 03/01/23 |
| 38 | */ |
| 39 | |
| 40 | |
| 41 | |
| 42 | import java.util.Random; |
| 43 | |
| 44 | /** |
| 45 | * An object that implements a cheesy pseudorandom permutation of the integers |
| 46 | * from zero to some user-specified value. (The permutation is a linear |
| 47 | * function.) |
| 48 | * |
| 49 | * @version 1.6 01/23/03 |
| 50 | * @author Josh Bloch |
| 51 | */ |
| 52 | class Permuter { |
| 53 | /** |
| 54 | * The size of the permutation. |
| 55 | */ |
| 56 | private int modulus; |
| 57 | |
| 58 | /** |
| 59 | * Nonnegative integer less than n that is relatively prime to m. |
| 60 | */ |
| 61 | private int multiplier; |
| 62 | |
| 63 | /** |
| 64 | * Pseudorandom nonnegative integer less than n. |
| 65 | */ |
| 66 | private int addend = 22; |
| 67 | |
| 68 | public Permuter(int n) { |
| 69 | if (n<0) { |
| 70 | throw new IllegalArgumentException(); |
| 71 | } |
| 72 | modulus = n; |
| 73 | if (n==1) { |
| 74 | return; |
| 75 | } |
| 76 | |
| 77 | // Initialize the multiplier and offset |
| 78 | multiplier = (int) Math.sqrt(n); |
| 79 | while (gcd(multiplier, n) != 1) { |
| 80 | if (++multiplier == n) { |
| 81 | multiplier = 1; |
| 82 | } |
| 83 | } |
| 84 | } |
| 85 | |
| 86 | /** |
| 87 | * Returns the integer to which this permuter maps the specified integer. |
| 88 | * The specified integer must be between 0 and n-1, and the returned |
| 89 | * integer will be as well. |
| 90 | */ |
| 91 | public int map(int i) { |
| 92 | return (multiplier * i + addend) % modulus; |
| 93 | } |
| 94 | |
| 95 | /** |
| 96 | * Calculate GCD of a and b, which are assumed to be non-negative. |
| 97 | */ |
| 98 | private static int gcd(int a, int b) { |
| 99 | while(b != 0) { |
| 100 | int tmp = a % b; |
| 101 | a = b; |
| 102 | b = tmp; |
| 103 | } |
| 104 | return a; |
| 105 | } |
| 106 | |
| 107 | /** |
| 108 | * Simple test. Takes modulus on command line and prints out permutation. |
| 109 | */ |
| 110 | public static void main(String[] args) { |
| 111 | int modulus = Integer.parseInt(args[0]); |
| 112 | Permuter p = new Permuter(modulus); |
| 113 | for (int i=0; i<modulus; i++) { |
| 114 | System.out.print(p.map(i)+" "); |
| 115 | } |
| 116 | System.out.println(); |
| 117 | } |
| 118 | } |
| 119 | |