---
name: "Algorithm::CheckDigits::M23_002"
section: "3pm"
platform: "linux"
package: "libalgorithm-checkdigits-perl"
version: "1.3.6-2"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Algorithm::CheckDigits::M23_002"
---

# Algorithm::CheckDigits::M23\_002(3pm)

compute check digits for Tax Identification Number (IE)

## NAME

CheckDigits::M23\_002 - compute check digits for Tax Identification Number (IE)

## SYNOPSIS

```
  use Algorithm::CheckDigits;
  $dni = CheckDigits('tin_ie');
  if ($dni->is_valid('8473625E')) {
        # do something
  }
  $cn = $dni->complete('1234567.W');
  # $cn = '1234567TW'
  $cd = $dni->checkdigit('1234577IA');
  # $cd = 'I'
  $bn = $dni->basenumber('1234577WW');
  # $bn = '1234577.W'
```

## DESCRIPTION

### 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.

## AUTHOR

Mathias Weidner, `"<mamawe@cpan.org>"`

## SEE ALSO

perl, CheckDigits, *https://ec.europa.eu/taxation\_customs/tin/*