1 /*
2 * (c) Copyright 2006-2020 by rapiddweller GmbH & Volker Bergmann. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, is permitted under the terms of the
6 * GNU General Public License.
7 *
8 * For redistributing this software or a derivative work under a license other
9 * than the GPL-compatible Free Software License as defined by the Free
10 * Software Foundation or approved by OSI, you must first obtain a commercial
11 * license to this software product from rapiddweller GmbH & Volker Bergmann.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
14 * WITHOUT A WARRANTY OF ANY KIND. ALL EXPRESS OR IMPLIED CONDITIONS,
15 * REPRESENTATIONS AND WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF
16 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE
17 * HEREBY EXCLUDED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
18 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
19 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
20 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
21 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
22 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
23 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
24 * POSSIBILITY OF SUCH DAMAGE.
25 */
26
27 package com.rapiddweller.benerator.util;
28
29 /**
30 * Provides utility methods for Luhn check digit calculation.<br/><br/>
31 * Created: 18.10.2009 10:06:01
32 *
33 * @author Volker Bergmann
34 * @since 0.6.0
35 */
36 public class LuhnUtil {
37
38 private LuhnUtil() {
39 }
40
41 /**
42 * Calculates the last digit expected for a number that passes the Luhn test,
43 * ignoring the last digit. This is useful for creating Luhn numbers.
44 * The actual evaluation if a number passes the test is done by
45 * {@link #luhnValid(CharSequence)}.
46 *
47 * @param number the number
48 * @return the char
49 * @see "http://en.wikipedia.org/wiki/Luhn_algorithm"
50 */
51 public static char requiredCheckDigit(CharSequence number) {
52 int sum = 0;
53 int multiplier = 2;
54 for (int i = number.length() - 2; i >= 0; i--) {
55 int digit = number.charAt(i) - '0';
56 int partialSum = digit * multiplier;
57 sum += (partialSum > 9 ? 1 + (partialSum % 10) : partialSum);
58 multiplier = 1 + (multiplier % 2);
59 }
60 return (char) ('0' + (10 - sum % 10) % 10);
61 }
62
63 /**
64 * Tests a number against the Luhn algorithm
65 *
66 * @param number the number
67 * @return the boolean
68 * @see #requiredCheckDigit(CharSequence) #requiredCheckDigit(CharSequence)
69 * @see "http://en.wikipedia.org/wiki/Luhn_algorithm"
70 */
71 public static boolean luhnValid(CharSequence number) {
72 return (requiredCheckDigit(number) == number.charAt(number.length() - 1));
73 }
74
75 }