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[verhoeff] / src / lib.rs
1 //! An implementation of the Verhoeff algorithm.
2 //!
3 //! This checksum algorithm is not particularly common (the simpler and somewhat inferior Luhn
4 //! algorithm is much more widely used, e.g. in credit card numbers), but it definitely gets some
5 //! use; for example, India’s Aadhaar biometric identity system uses 12-digit numbers as the ID
6 //! number, with the final digit being a Verhoeff checksum.
7 //!
8 //! Background reading: <https://en.wikipedia.org/wiki/Verhoeff_algorithm>
9
10 #![cfg_attr(not(feature = "std"), no_std)]
11
12 #[cfg(feature = "alloc")]
13 extern crate alloc;
14
15 /// The multiplication table.
16 static D: [[u8; 10]; 10] = [
17 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
18 [1, 2, 3, 4, 0, 6, 7, 8, 9, 5],
19 [2, 3, 4, 0, 1, 7, 8, 9, 5, 6],
20 [3, 4, 0, 1, 2, 8, 9, 5, 6, 7],
21 [4, 0, 1, 2, 3, 9, 5, 6, 7, 8],
22 [5, 9, 8, 7, 6, 0, 4, 3, 2, 1],
23 [6, 5, 9, 8, 7, 1, 0, 4, 3, 2],
24 [7, 6, 5, 9, 8, 2, 1, 0, 4, 3],
25 [8, 7, 6, 5, 9, 3, 2, 1, 0, 4],
26 [9, 8, 7, 6, 5, 4, 3, 2, 1, 0],
27 ];
28
29 /// The permutation table.
30 static P: [[u8; 10]; 8] = [
31 [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
32 [1, 5, 7, 6, 2, 8, 3, 0, 9, 4],
33 [5, 8, 0, 3, 7, 9, 6, 1, 4, 2],
34 [8, 9, 1, 6, 0, 4, 3, 5, 2, 7],
35 [9, 4, 5, 3, 1, 2, 6, 8, 7, 0],
36 [4, 2, 8, 6, 5, 7, 3, 9, 0, 1],
37 [2, 7, 9, 3, 8, 0, 6, 4, 1, 5],
38 [7, 0, 4, 6, 9, 1, 3, 2, 5, 8],
39 ];
40
41 /// The inverse table.
42 static INV: [u8; 10] = [0, 4, 3, 2, 1, 5, 6, 7, 8, 9];
43
44 /// Methods to perform the Verhoeff algorithm.
45 ///
46 /// This is implemented for strings (which must contain only the ASCII digits 0–9) and u8 slices
47 /// (which must contain only the numbers 0–9).
48 ///
49 /// ## Examples
50 ///
51 /// ```
52 /// use verhoeff::Verhoeff;
53 /// assert_eq!("12345".calculate_verhoeff_check_digit(), 1);
54 /// assert!("123451".validate_verhoeff_check_digit());
55 /// ```
56 pub trait Verhoeff {
57 /// Confirm that the digits are valid and that the last is the correct check digit.
58 ///
59 /// If any digit is not valid (a character other than ASCII digits 0–9 in strings, or a
60 /// number greater than nine in `u8` slices), it returns false.
61 fn validate_verhoeff_check_digit(&self) -> bool;
62
63 /// Calculate the check digit for this input.
64 ///
65 /// If any digit is not valid (a character other than ASCII digits 0–9 in strings, or a
66 /// number greater than nine in `u8` slices), it will panic.
67 ///
68 /// The return value is an integer in the range 0–9.
69 fn calculate_verhoeff_check_digit(&self) -> u8;
70 }
71
72 impl Verhoeff for str {
73 fn validate_verhoeff_check_digit(&self) -> bool {
74 let mut c = 0;
75 for (i, digit) in self.bytes().rev().enumerate() {
76 let digit = match digit {
77 b'0'..=b'9' => digit - b'0',
78 _ => return false,
79 };
80 c = D[c][P[i % 8][digit as usize] as usize] as usize;
81 }
82
83 c == 0
84 }
85
86 fn calculate_verhoeff_check_digit(&self) -> u8 {
87 let mut c = 0;
88 for (i, digit) in self.bytes().rev().enumerate() {
89 assert!(
90 matches!(digit, b'0'..=b'9'),
91 "number string contains a non-digit character",
92 );
93 c = D[c][P[(i + 1) % 8][(digit - b'0') as usize] as usize] as usize;
94 }
95
96 INV[c]
97 }
98 }
99
100 impl Verhoeff for [u8] {
101 fn validate_verhoeff_check_digit(&self) -> bool {
102 let mut c = 0;
103 for (i, &digit) in self.iter().rev().enumerate() {
104 if digit > 9 {
105 return false;
106 }
107 c = D[c][P[i % 8][digit as usize] as usize] as usize;
108 }
109
110 c == 0
111 }
112
113 fn calculate_verhoeff_check_digit(&self) -> u8 {
114 let mut c = 0;
115 for (i, &digit) in self.iter().rev().enumerate() {
116 assert!(digit < 10, "number sequence contains a value above nine");
117 c = D[c][P[(i + 1) % 8][digit as usize] as usize] as usize;
118 }
119
120 INV[c]
121 }
122 }
123
124 /// A convenience trait for mutable methods pertaining to the Verhoeff algorithm.
125 ///
126 #[cfg_attr(
127 feature = "alloc",
128 doc = " This is implemented for `String` and `Vec<u8>`.",
129 )]
130 #[cfg_attr(
131 not(feature = "alloc"),
132 doc = " This is normally implemented for `String` and `Vec<u8>`, but you’ve you’ve disabled \
133 the alloc feature, so it’s not implemented on anything out of the box.",
134 )]
135 pub trait VerhoeffMut {
136 /// A convenience method to apply the Verhoeff algorithm in-place.
137 ///
138 /// ## Example
139 ///
140 /// ```
141 /// # #[cfg(feature = "alloc")] {
142 /// use verhoeff::VerhoeffMut;
143 /// let mut digits = String::from("12345");
144 /// digits.push_verhoeff_check_digit();
145 /// assert_eq!(digits, "123451");
146 /// # }
147 /// ```
148 fn push_verhoeff_check_digit(&mut self);
149 }
150
151 #[cfg(feature = "alloc")]
152 impl VerhoeffMut for alloc::string::String {
153 fn push_verhoeff_check_digit(&mut self) {
154 self.push(char::from(b'0' + self.calculate_verhoeff_check_digit()));
155 }
156 }
157
158 #[cfg(feature = "alloc")]
159 impl VerhoeffMut for alloc::vec::Vec<u8> {
160 /// A convenience method to apply the Verhoeff algorithm in-place.
161 ///
162 /// ## Example
163 ///
164 /// ```
165 /// use verhoeff::VerhoeffMut;
166 /// let mut digits = vec![1, 2, 3, 4, 5];
167 /// digits.push_verhoeff_check_digit();
168 /// assert_eq!(digits, [1, 2, 3, 4, 5, 1]);
169 /// ```
170 fn push_verhoeff_check_digit(&mut self) {
171 self.push(self.calculate_verhoeff_check_digit());
172 }
173 }
174
175 /// A convenience method to calculate the Verhoeff algorithm check digit.
176 ///
177 /// You can pass in a `&str` or a `&[u8]`, and get back a number in the range 0–9.
178 ///
179 /// This is equivalent to calling [`Verhoeff::calculate_verhoeff_check_digit`].
180 /// It will panic if the input is not comprised of appropriate digits.
181 #[inline]
182 pub fn calculate<T: Verhoeff + ?Sized>(input: &T) -> u8 {
183 input.calculate_verhoeff_check_digit()
184 }
185
186 /// A convenience method to validate against the Verhoeff algorithm.
187 ///
188 /// The check digit is presumed to be at the end of the input.
189 ///
190 /// You can pass in a `&str` or a `&[u8]`.
191 ///
192 /// This is equivalent to calling [`Verhoeff::validate_verhoeff_check_digit`].
193 /// It will return false if the input is not comprised of appropriate digits.
194 #[inline]
195 pub fn validate<T: Verhoeff + ?Sized>(input: &T) -> bool {
196 input.validate_verhoeff_check_digit()
197 }
198
199 #[test]
200 fn test() {
201 for full in [
202 "0",
203 "2363",
204 "758722",
205 "123451",
206 "1428570",
207 "1234567890120",
208 "84736430954837284567892",
209 ] {
210 let sans_check_digit = &full[..full.len() - 1];
211 let expected_check_digit = full.chars().last().unwrap() as u32 as u8 - b'0';
212 let actual_check_digit = calculate(sans_check_digit);
213 if expected_check_digit != actual_check_digit {
214 panic!(
215 "On {}, expected check digit {} but calculated {}",
216 sans_check_digit, expected_check_digit, actual_check_digit,
217 );
218 }
219 if !validate(full) {
220 panic!("{} failed to validate", full);
221 }
222 #[cfg(feature = "alloc")]
223 {
224 let mut new = alloc::string::String::from(sans_check_digit);
225 new.push_verhoeff_check_digit();
226 assert_eq!(new, full);
227 }
228 }
229 for full in [
230 &[0],
231 &[2, 3, 6, 3],
232 &[7, 5, 8, 7, 2, 2],
233 &[1, 2, 3, 4, 5, 1],
234 &[1, 4, 2, 8, 5, 7, 0],
235 &[1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 0],
236 &[
237 8, 4, 7, 3, 6, 4, 3, 0, 9, 5, 4, 8, 3, 7, 2, 8, 4, 5, 6, 7, 8, 9, 2,
238 ],
239 ] as [&[u8]; 7] {
240 let sans_check_digit = &full[..full.len() - 1];
241 let expected_check_digit = *full.iter().last().unwrap();
242 let actual_check_digit = calculate(sans_check_digit);
243 if expected_check_digit != actual_check_digit {
244 panic!(
245 "On {:?}, expected check digit {:?} but calculated {:?}",
246 sans_check_digit, expected_check_digit, actual_check_digit,
247 );
248 }
249 if !validate(full) {
250 panic!("{:?} failed to validate", full);
251 }
252 #[cfg(feature = "alloc")]
253 {
254 let mut new = alloc::vec::Vec::from(sans_check_digit);
255 new.push_verhoeff_check_digit();
256 assert_eq!(new, full);
257 }
258 }
259 assert!(!validate("122451"));
260 assert!(!"128451".validate_verhoeff_check_digit());
261 assert!(![1, 2, 4, 3, 5, 1].validate_verhoeff_check_digit());
262 }
263
264 #[test]
265 fn malformed_inputs_1() {
266 assert!([].validate_verhoeff_check_digit());
267 assert!("".validate_verhoeff_check_digit());
268 assert!(![1, 2, 3, 4, 10, 5, 6].validate_verhoeff_check_digit());
269 assert!(!validate("1234∞56"));
270 }
271
272 #[test]
273 #[should_panic]
274 fn malformed_inputs_2() {
275 [1, 2, 3, 4, 10, 5, 6].calculate_verhoeff_check_digit();
276 }
277
278 #[test]
279 #[should_panic]
280 fn malformed_inputs_3() {
281 calculate("1234∞56");
282 }