Verhoeff36 in Lua

ver36.lua

#!/usr/bin/lua

do
  local N = 18

  -- Group operation in D18
  local d18_op = {}
  for i = 1, N do
    d18_op[i] = {}
    for j = 1, N do
      d18_op[i][j] = 1 + (i + j - 2) % N
    end
  end
  for i = 1, N do
    for j = N+1, 2*N do
      d18_op[i][j] = 1+N + (i + j - 2) % N
    end
  end
  for i = N+1, 2*N do
    d18_op[i] = {}
    for j = 1, N do
      d18_op[i][j] = 1+N + (i - j) % N
    end
  end
  for i = N+1, 2*N do
    for j = N+1, 2*N do
      d18_op[i][j] = 1 + (i - j) % N
    end
  end

  -- Inverse element
  local d18_inv = {}
  d18_inv[1] = 1
  for i = 2, N do
    d18_inv[i] = N-i+2
  end
  for i = N+1, 2*N do
    d18_inv[i] = i
  end

  -- The permutation
  local perm = {}
  do
    local b, i, p = {}, 1, {
      30,1,33,12,36,21,8,28,3,5,20,29,31,2,6,13,4,10,17,
      23,7,34,9,25,27,22,15,11,35,32,16,26,18,14,24,19
    }
    while i <= #p do
      local c, l = {}, 0
      while not b[i] do
        l = l + 1
        c[l] = p[i]
        b[i] = true
        i = p[i]
      end
      for j = 1, #c do
        perm[c[j]] = {}
        for k = 1, #c do
          perm[c[j]][k] = c[1 + (j + k - 2) % #c]
        end
      end
      i = 1; while i <= #p and b[i] do i = i + 1 end
    end
  end

  -- ASCII translation tables
  local a2i = {}
  for i = 0x00, 0xff do a2i[i] = nil end
  for i = 0x30, 0x39 do a2i[i] = i - 0x30 + 1 end
  for i = 0x41, 0x5a do a2i[i] = i - 0x41 + 11 end
  for i = 0x61, 0x7a do a2i[i] = i - 0x61 + 11 end
  local i2a = {}
  for i = 0, 10 do i2a[i] = i + 0x30 end
  for i =10,2*N do i2a[i] = i + 0x41 - 10 end

  -- Calculate check digit
  local function ver(str, i)
    local c, l = 1, #str
    while l > 0 do
      local ch = a2i[str:byte(l)]
      if ch then
        c = d18_op[c][perm[ch][1+(i-1)%#(perm[ch])]]
        i = i + 1
      end
      l = l - 1
    end
    return c
  end
  
  -- Verify correctness of check digit
  local function verify(str)
    return ver(str, 1) == 1
  end

  -- Append check digit to given string
  local function append(str)
    local c = d18_inv[ver(str, 2)]
    c = c + 0x30 - 1
    if c > 0x39 then c = c + 7 end
    return str .. string.format("%c", c)
  end

  -- Act as command line utility
  if arg then
    local ap, lt = false, false
    for i = 1,#arg do
      if not lt and (arg[i]=="-a" or arg[i]=="-c" or arg[i]=="--") then
        if arg[i] == "-a" then ap = true end
        if arg[i] == "-c" then ap = false end
        if arg[i] == "--" then lt = true end
      else
        if ap then
          print(append(arg[i]))
        else
          if verify(arg[i]) then
            print(arg[i], "OK")
          else
            print(arg[i], "FAIL")
          end
        end
      end
    end
  end

  -- Export public interface as module
  return {
    verify = verify,
    append = append
  }
end