Function: luhnMod10()

luhnMod10(digits): number

Internal

The Luhn sum (mod 10) of a numeric string, doubling every second digit from the right. Used to verify (or deliberately break) an NPI check digit.

Parameters

digits

string

A string of decimal digits.

Returns

number

The Luhn sum modulo 10 (0 ⇒ the string passes the Luhn check).