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.\" ========================================================================
.\"
.IX Title "Algorithm::CheckDigits::M23_002 3pm"
.TH Algorithm::CheckDigits::M23_002 3pm "2022-10-13" "perl v5.34.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH "NAME"
CheckDigits::M23_002 \- compute check digits for Tax Identification Number (IE)
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  use Algorithm::CheckDigits;
\&
\&  $dni = CheckDigits(\*(Aqtin_ie\*(Aq);
\&
\&  if ($dni\->is_valid(\*(Aq8473625E\*(Aq)) {
\&        # do something
\&  }
\&
\&  $cn = $dni\->complete(\*(Aq1234567.W\*(Aq);
\&  # $cn = \*(Aq1234567TW\*(Aq
\&
\&  $cd = $dni\->checkdigit(\*(Aq1234577IA\*(Aq);
\&  # $cd = \*(AqI\*(Aq
\&
\&  $bn = $dni\->basenumber(\*(Aq1234577WW\*(Aq);
\&  # $bn = \*(Aq1234577.W\*(Aq
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
.SS "\s-1ALGORITHM\s0"
.IX Subsection "ALGORITHM"
The irish \s-1TIN\s0 (Tax Identification Number) or \s-1VAT\s0 Regstration Number
consists of 7 digits, a letter in the range from 'A' \- 'W' as checksum,
and an optionally letter in the range from 'A' \- 'I' or the letter 'W'.
.IP "1." 4
In reverse order, each digit is multiplied by a weight started at 2.
(i.e. the number left from the check digit is multiplied with 2,
the next with 3 and so on).
.IP "2." 4
If there is an optional letter following the checksum letter (position 9),
this letter is mapped to a numeric value based on the following mapping:
\&\*(L"A\*(R" = 1, \*(L"B\*(R" = 2, ... \*(L"H\*(R" = 8, \*(L"I\*(R" = 9. \*(L"W\*(R" or absence of this letter
means a value of 0. This numeric value is multiplied with 9.
.IP "3." 4
All products from step 1 and 2 are added.
.IP "4." 4
The check digit is the sum from step 3 modulo 23. This number is
expressed as the corresponding letter from the alphabet where A\-V
correspond to 1\-22 and W stands for check digit 0.
.SS "\s-1METHODS\s0"
.IX Subsection "METHODS"
.IP "is_valid($number)" 4
.IX Item "is_valid($number)"
Returns true only if \f(CW$number\fR complies with the rules given above
and there is a valid check digit at position eight.
.Sp
Returns false otherwise,
.IP "complete($number)" 4
.IX Item "complete($number)"
The check digit for \f(CW$number\fR is computed and inserted at position eight
of \f(CW$number\fR.
.Sp
Returns the complete number with check digit or '' if \f(CW$number\fR
does not consist solely of digits and an optional letter at position nine.
.IP "basenumber($number)" 4
.IX Item "basenumber($number)"
Returns the basenumber of \f(CW$number\fR if \f(CW$number\fR has a valid check
digit. As a placeholder for the checksum a point ('.') is inserted
at position eight when the checksum contains the optional letter
at position nine.
.Sp
Return '' otherwise.
.IP "checkdigit($number)" 4
.IX Item "checkdigit($number)"
Returns the checkdigit of \f(CW$number\fR if \f(CW$number\fR has a valid check
digit.
.Sp
Return '' otherwise.
.SS "\s-1EXPORT\s0"
.IX Subsection "EXPORT"
None by default.
.SH "AUTHOR"
.IX Header "AUTHOR"
Mathias Weidner, \f(CW\*(C`<mamawe@cpan.org>\*(C'\fR
.SH "SEE ALSO"
.IX Header "SEE ALSO"
perl,
CheckDigits,
\&\fIhttps://ec.europa.eu/taxation_customs/tin/\fR