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# Manual Reference Pages  -  ALGORITHM::CHECKDIGITS::MXX_005 (3)

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### NAME

CheckDigits::MXX_005 - compute check digits for ESR9 (CH)

### SYNOPSIS

use Algorithm::CheckDigits;

\$esr = CheckDigits(esr9);

if (\$esr->is_valid(123456786)) {
# do something
}

\$cn = \$esr->complete(12345678);
# \$cn = 123456786

\$cd = \$esr->checkdigit(123456786);
# \$cd = 6

\$bn = \$esr->basenumber(123456786);
# \$bn = 12345678

### DESCRIPTION

#### ALGORITHM

 1. Digits are processed left to right. For the first digit applies the balance is 0. 2. The new balance is taken from the balance table according to the current balance (row) and the digit (column). 3. The check digit is the difference from the last balance to 10 taken modulo 10.

#### METHODS

 is_valid(\$number) Returns true only if \$number consists solely of numbers and the last digit is a valid check digit according to the algorithm given above. Returns false otherwise, complete(\$number) The check digit for \$number is computed and concatenated to the end of \$number. Returns the complete number with check digit or ’’ if \$number does not consist solely of digits and spaces. basenumber(\$number) Returns the basenumber of \$number if \$number has a valid check digit. Return ’’ otherwise. checkdigit(\$number) Returns the checkdigit of \$number if \$number has a valid check digit. Return ’’ otherwise.

None by default.

### AUTHOR

Mathias Weidner, <mamawe@cpan.org>