1 /*
2 * Copyright (C) 2018 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 #include "utils/checksum.h"
18 #include "utils/strings/numbers.h"
19
20 namespace libtextclassifier3 {
21
VerifyLuhnChecksum(const std::string & input,bool ignore_whitespace)22 bool VerifyLuhnChecksum(const std::string& input, bool ignore_whitespace) {
23 int sum = 0;
24 int num_digits = 0;
25 bool is_odd = true;
26
27 // http://en.wikipedia.org/wiki/Luhn_algorithm
28 static const int kPrecomputedSumsOfDoubledDigits[] = {0, 2, 4, 6, 8,
29 1, 3, 5, 7, 9};
30 for (int i = input.size() - 1; i >= 0; i--) {
31 const char c = input[i];
32 if (ignore_whitespace && c == ' ') {
33 continue;
34 }
35 if (!isdigit(c)) {
36 return false;
37 }
38 ++num_digits;
39 const int digit = c - '0';
40 if (is_odd) {
41 sum += digit;
42 } else {
43 sum += kPrecomputedSumsOfDoubledDigits[digit];
44 }
45 is_odd = !is_odd;
46 }
47 return (num_digits > 1 && sum % 10 == 0);
48 }
49
50 } // namespace libtextclassifier3
51