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.\" ========================================================================
.\"
.IX Title "Algorithm::CheckDigits::M11_001 3pm"
.TH Algorithm::CheckDigits::M11_001 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::M11_001 \- compute check digits for ISBN, ISSN, VAT RN
(PT), HKID (HK), Wagon number (BR), NHS (GB), VAT (SL)
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&  use Algorithm::CheckDigits;
\&
\&  $isbn = CheckDigits(\*(Aqisbn\*(Aq);
\&
\&  if ($isbn\->is_valid(\*(Aq3\-88229\-192\-3\*(Aq)) {
\&        # do something
\&  }
\&
\&  $cn = $isbn\->complete(\*(Aq3\-88229\-192\-\*(Aq);
\&  # $cn = \*(Aq3\-88229\-192\-3\*(Aq
\&
\&  $cd = $isbn\->checkdigit(\*(Aq3\-88229\-192\-3\*(Aq);
\&  # $cd = \*(Aq3\*(Aq
\&
\&  $bn = $isbn\->basenumber(\*(Aq3\-88229\-192\-3\*(Aq);
\&  # $bn = \*(Aq3\-88229\-192\-\*(Aq
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
.SS "\s-1ALGORITHM\s0"
.IX Subsection "ALGORITHM"
.IP "1." 4
The sequence of digits is processed right to left.
Every digit is multiplied with their position in the sequence (i.e.
the digit left to the check digit has the weight 2 then 3 etc.).
.Sp
With a Hongkong \s-1ID\s0 (hkid) the leftmost char is replaced with its
position in the alphabet and then multiplied with 8 (its weight).
.IP "2." 4
The sum of all products is computed.
.IP "3." 4
The sum of step 2 is taken modulo 11.
.IP "4." 4
The checkdigit is the difference of the sum from step 3 to eleven
under the following conditions:
.RS 4
.IP "isbn,issn" 8
.IX Item "isbn,issn"
If the difference is 10, the check digit is 'X'.
.Sp
If the difference is 11, the check digit is 0.
.IP "ustid_pt" 8
.IX Item "ustid_pt"
If the difference is greater then 9, the check digit is '0'.
.IP "hkid" 8
.IX Item "hkid"
If the difference is 10, the check digit is 'A'.
.Sp
If the difference is 11, the check digit is 0.
.IP "wagonnr_br" 8
.IX Item "wagonnr_br"
If the difference is 10, the check digit is 0.
.Sp
If the difference is 11, the check digit is 1.
.IP "nhs_gb" 8
.IX Item "nhs_gb"
If the difference is 10, the number would not be taken.
.Sp
If the difference is 11, the check digit is 0.
.IP "vat_sl" 8
.IX Item "vat_sl"
This is a little bit unclear, don't trust on the method for this type.
.RE
.RS 4
.RE
.SS "\s-1METHODS\s0"
.IX Subsection "METHODS"
.IP "is_valid($number)" 4
.IX Item "is_valid($number)"
Returns true only if \f(CW$number\fR consists solely of numbers and the last digit
is a valid check digit according to the algorithm given above.
.Sp
Returns false otherwise,
.IP "complete($number)" 4
.IX Item "complete($number)"
The check digit for \f(CW$number\fR is computed and concatenated to the end
of \f(CW$number\fR.
.Sp
Returns the complete number with check digit or '' if \f(CW$number\fR
does not consist solely of digits and spaces.
.IP "basenumber($number)" 4
.IX Item "basenumber($number)"
Returns the basenumber of \f(CW$number\fR if \f(CW$number\fR has a valid check
digit.
.Sp
Return '' otherwise.
.IP "checkdigit($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,
\&\fIwww.pruefziffernberechnung.de\fR.