ALGORITHM¶

The irish TIN (Tax Identification Number) or VAT 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'.

1.

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).

2.

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: "A" = 1, "B" = 2, ... "H" = 8, "I" = 9. "W" or absence of this letter means a value of 0. This numeric value is multiplied with 9.

3.

All products from step 1 and 2 are added.

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.

METHODS¶

is_valid($number)

Returns true only if $number complies with the rules given above and there is a valid check digit at position eight.

Returns false otherwise,

complete($number)

The check digit for $number is computed and inserted at position eight of $number.

Returns the complete number with check digit or '' if $number does not consist solely of digits and an optional letter at position nine.

basenumber($number)

Returns the basenumber of $number if $number 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.

Return '' otherwise.

checkdigit($number)

Returns the checkdigit of $number if $number has a valid check digit.

Return '' otherwise.

EXPORT¶

None by default.