1Algorithm::LUHN(3)    User Contributed Perl Documentation   Algorithm::LUHN(3)
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NAME

6       Algorithm::LUHN - Calculate the Modulus 10 Double Add Double checksum
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SYNOPSIS

9         use Algorithm::LUHN qw/check_digit is_valid/;
10
11         $c = check_digit("43881234567");
12         print "It works\n" if is_valid("43881234567$c");
13
14         $c = check_digit("A2C4E6G8"); # this will cause an error
15
16         print "Valid LUHN characters are:\n";
17         my %vc = Algorithm::LUHN::valid_chars();
18         for (sort keys %vc) {
19           print "$_ => $vc{$_}\n";
20         }
21
22         Algorithm::LUHN::valid_chars(map {$_ => ord($_)-ord('A')+10} A..Z);
23         $c = check_digit("A2C4E6G8");
24         print "It worked again\n" if is_valid("A2C4E6G8$c");
25

DESCRIPTION

27       This module calculates the Modulus 10 Double Add Double checksum, also
28       known as the LUHN Formula. This algorithm is used to verify credit card
29       numbers and Standard & Poor's security identifiers such as CUSIP's and
30       CSIN's.
31
32       You can find plenty of information about the algorithm by searching the
33       web for "modulus 10 double add double".
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FUNCTION

36       is_valid CHECKSUMMED_NUM
37           This function takes a credit-card number and returns true if the
38           number passes the LUHN check.
39
40           Ie it returns true if the final character of CHECKSUMMED_NUM is the
41           correct checksum for the rest of the number and false if not.
42           Obviously the final character does not factor into the checksum
43           calculation. False will also be returned if NUM contains in an
44           invalid character as defined by valid_chars(). If NUM is not valid,
45           $Algorithm::LUHN::ERROR will contain the reason.
46
47           This function is equivalent to
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49             substr $N,length($N)-1 eq check_digit(substr $N,0,length($N)-1)
50
51           For example, "4242 4242 4242 4242" is a valid Visa card number,
52           that is provided for test purposes. The final digit is '2', which
53           is the right check digit. If you change it to a '3', it's not a
54           valid card number. Ie:
55
56               is_valid('4242424242424242');   # true
57               is_valid('4242424242424243');   # false
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59       check_digit NUM
60           This function returns the checksum of the given number. If it
61           cannot calculate the check_digit it will return undef and set
62           $Algorithm::LUHN::ERROR to contain the reason why.
63
64       valid_chars LIST
65           By default this module only recognizes 0..9 as valid characters,
66           but sometimes you want to consider other characters as valid, e.g.
67           Standard & Poor's identifers may contain 0..9, A..Z, @, #, *. This
68           function allows you to add additional characters to the accepted
69           list.
70
71           LIST is a mapping of "character" => "value".  For example, Standard
72           & Poor's maps A..Z to 10..35 so the LIST to add these valid
73           characters would be (A, 10, B, 11, C, 12, ...)
74
75           Please note that this adds or re-maps characters, so any characters
76           already considered valid but not in LIST will remain valid.
77
78           If you do not provide LIST, this function returns the current valid
79           character map.
80

SEE ALSO

82       Algorithm::CheckDigits provides a front-end to a large collection of
83       modules for working with check digits.
84
85       Business::CreditCard provides three functions for checking credit card
86       numbers. Business::CreditCard::Object provides an OO interface to those
87       functions.
88
89       Business::CardInfo provides a class for holding credit card details,
90       and has a type constraint on the card number, to ensure it passes the
91       LUHN check.
92
93       Business::CCCheck provides a number of functions for checking credit
94       card numbers.
95
96       Regexp::Common supports combined LUHN and issuer checking against a
97       card number.
98
99       Algorithm::Damm implements a different kind of check digit algorithm,
100       the Damm algorithm <https://en.wikipedia.org/wiki/Damm_algorithm>
101       (Damm, not Damn).
102
103       Math::CheckDigits implements yet another approach to check digits.
104
105       I have also written a review of LUHN modules
106       <http://neilb.org/reviews/luhn.html>, which covers them in more detail
107       than this section.
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REPOSITORY

110       <https://github.com/neilb/Algorithm-LUHN>
111

AUTHOR

113       This module was written by Tim Ayers
114       (http://search.cpan.org/search?author=TAYERS).
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117       Copyright (c) 2001 Tim Ayers. All rights reserved.
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LICENSE

120       This program is free software; you can redistribute it and/or modify it
121       under the same terms as Perl itself.
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125perl v5.34.0                      2022-01-20                Algorithm::LUHN(3)
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