Module:Verhoeff

This module implements the Verhoeff check digit algorithm in Lua.

Usage

verhoeff_gen(str)

Generates a Verhoeff algorithm check digit for str and returns the digit string with check digit appended.

verhoeff_verify(str)

Verifies the check digit at the end of str according to the Verhoeff algorithm, returning true iff successful.

---

verhoeff_mult =
{
    {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
    {1, 2, 3, 4, 0, 6, 7, 8, 9, 5},
    {2, 3, 4, 0, 1, 7, 8, 9, 5, 6},
    {3, 4, 0, 1, 2, 8, 9, 5, 6, 7},
    {4, 0, 1, 2, 3, 9, 5, 6, 7, 8},
    {5, 9, 8, 7, 6, 0, 4, 3, 2, 1},
    {6, 5, 9, 8, 7, 1, 0, 4, 3, 2},
    {7, 6, 5, 9, 8, 2, 1, 0, 4, 3},
    {8, 7, 6, 5, 9, 3, 2, 1, 0, 4},
    {9, 8, 7, 6, 5, 4, 3, 2, 1, 0}
}
verhoeff_perm = {1, 5, 7, 6, 2, 8, 3, 0, 9, 4}
verhoeff_inv = {0, 4, 3, 2, 1, 5, 6, 7, 8, 9}

function verhoeff(xs_r)
  xs = xs_r:reverse()
  c = 0
  for i=1,xs:len(),1
  do
    p = xs:sub(i,i)
    for j=1,((i-1)%8),1
    do
      p = verhoeff_perm[p+1]
    end
    c = verhoeff_mult[c+1][p+1]
  end
  return c
end

function verhoeff_verify(str)
  return verhoeff(str) == 0
end

function verhoeff_gen(str)
  return str..verhoeff_inv[verhoeff(str.."0")+1]
end

function identity(x) return x end

id_to_n = { R=1, L=2, S=3, A=3, E=4 }

return {verhoeff_verify=verhoeff_verify, verhoeff_gen=verhoeff_gen}