Verhoeff.java

/**
 * Copyright © 2002 Instituto Superior Técnico
 *
 * This file is part of FenixEdu Academic.
 *
 * FenixEdu Academic is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * FenixEdu Academic 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with FenixEdu Academic.  If not, see <http://www.gnu.org/licenses/>.
 */
package org.fenixedu.academic.domain.util;

/**
 * @see <a href="http://en.wikipedia.org/wiki/Verhoeff_algorithm/">More Info</a>
 * @see <a href="http://en.wikipedia.org/wiki/Dihedral_group">Dihedral Group</a>
 * @see <a href="http://mathworld.wolfram.com/DihedralGroupD5.html">Dihedral Group Order 10</a>
 * @author Colm Rice
 */
public class Verhoeff {

    // The multiplication table
    static int[][] d = new int[][] { { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }, { 1, 2, 3, 4, 0, 6, 7, 8, 9, 5 },
            { 2, 3, 4, 0, 1, 7, 8, 9, 5, 6 }, { 3, 4, 0, 1, 2, 8, 9, 5, 6, 7 }, { 4, 0, 1, 2, 3, 9, 5, 6, 7, 8 },
            { 5, 9, 8, 7, 6, 0, 4, 3, 2, 1 }, { 6, 5, 9, 8, 7, 1, 0, 4, 3, 2 }, { 7, 6, 5, 9, 8, 2, 1, 0, 4, 3 },
            { 8, 7, 6, 5, 9, 3, 2, 1, 0, 4 }, { 9, 8, 7, 6, 5, 4, 3, 2, 1, 0 } };

    // The permutation table
    static int[][] p = new int[][] { { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 }, { 1, 5, 7, 6, 2, 8, 3, 0, 9, 4 },
            { 5, 8, 0, 3, 7, 9, 6, 1, 4, 2 }, { 8, 9, 1, 6, 0, 4, 3, 5, 2, 7 }, { 9, 4, 5, 3, 1, 2, 6, 8, 7, 0 },
            { 4, 2, 8, 6, 5, 7, 3, 9, 0, 1 }, { 2, 7, 9, 3, 8, 0, 6, 4, 1, 5 }, { 7, 0, 4, 6, 9, 1, 3, 2, 5, 8 } };

    // The inverse table
    static int[] inv = { 0, 4, 3, 2, 1, 5, 6, 7, 8, 9 };

    /*
     * For a given number generates a Verhoeff digit
     */
    public static String generateVerhoeff(String num) {

        int c = 0;
        int[] myArray = StringToReversedIntArray(num);

        for (int i = 0; i < myArray.length; i++) {
            c = d[c][p[((i + 1) % 8)][myArray[i]]];
        }

        return Integer.toString(inv[c]);
    }

    /*
     * Validates that an entered number is Verhoeff compliant. NB: Make sure the
     * check digit is the last one.
     */
    public static boolean validateVerhoeff(String num) {

        int c = 0;
        int[] myArray = StringToReversedIntArray(num);

        for (int i = 0; i < myArray.length; i++) {
            c = d[c][p[(i % 8)][myArray[i]]];
        }

        return (c == 0);
    }

    /*
     * Converts a string to a reversed integer array.
     */
    private static int[] StringToReversedIntArray(String num) {

        int[] myArray = new int[num.length()];

        for (int i = 0; i < num.length(); i++) {
            myArray[i] = Integer.parseInt(num.substring(i, i + 1));
        }

        myArray = Reverse(myArray);

        return myArray;

    }

    /*
     * Reverses an int array
     */
    private static int[] Reverse(int[] myArray) {
        int[] reversed = new int[myArray.length];

        for (int i = 0; i < myArray.length; i++) {
            reversed[i] = myArray[myArray.length - (i + 1)];
        }

        return reversed;
    }

}