Method: Gtiny::CheckDigitCalculators.gs1

Defined in:
lib/gtiny/check_digit_calculators.rb

.gs1(digits) ⇒ String

Calculate the check digit for any GTIN or ISBN-13.

There’s a great visualization of this algorithm here: www.gs1.org/services/how-calculate-check-digit-manually

Parameters:

  • digits (String) —

    • the barcode digits (without the check digit)

Returns:

  • (String) —

    • the computed check digit



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# File 'lib/gtiny/check_digit_calculators.rb', line 13

def self.gs1(digits)
  sum = digits.reverse.each_char.with_index.sum do |digit, idx|
    multiplier = (idx % 2).zero? ? 3 : 1
    multiplier * digit.to_i
  end

  check_digit = (10 - sum) % 10
  check_digit.to_s
end