Module:Verhoeff

Documentation for this module may be created at Module:Verhoeff/doc

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 }

function wrm_idproc(str_r, func, pp, gc)
  str_stripped = str_r:upper():gsub("^WRM%-?", "")
  prefix = str_stripped:match("^[RLSAE]")
  res = func(str_stripped:gsub("([RLSAE]?)(%d+)",
    function(p, ds, x)
      return (gc and "%u%05u" or "%u%06u"):format(id_to_n[p] or 0, ds)
    end))
  if pp
  then
    return ("WRM-%s%04u"):format(prefix or "", res:sub(2))
  else
    return res
  end
end

function wrm_gencheck(str_r)
  return wrm_idproc(str_r, verhoeff_gen, true, true)
end

function wrm_verifycheck(str_r)
  return wrm_idproc(str_r, verhoeff_verify, false, false)
end

local p = {gen=wrm_gencheck, verify=wrm_verifycheck}
return p