var Ver36 = function() {
  "use strict";
  var N = 18, N2 = N*2;
  var d18_op;   // D18 group operation table
  var d18_inv;  // D18 group inverse
  var perm;     // the permutation decomposed into cycles
  var a2i,i2a;  // ASCII translation tables
  var NA=0xff;  // invalid digit marker in ASCII table

  // initialization code
  (function() {
    var A8 = typeof Uint8Array != 'undefined' ? Uint8Array : Array;
    // prepare Cayley table for D18 group
    d18_op = new A8(N2*N2);
    var i, j;
    for (i = 0; i < N; i++)
      for (j = 0; j < N; j++)
        d18_op[N2*i+j] = (i + j) % N;
    for (i = 0; i < N; i++)
      for (j = N; j < N2; j++)
        d18_op[N2*i+j] = N + (i + j) % N;
    for (i = N; i < N2; i++)
      for (j = 0; j < N; j++)
        d18_op[N2*i+j] = N + (i - j) % N;
    for (i = N; i < N2; i++)
      for (j = N; j < N2; j++)
        d18_op[N2*i+j] = (N + i - j) % N;
    // prepare inverse element table
    d18_inv = new A8(N2);
    d18_inv[0] = 0;
    for (i = 1; i < N; i++)
      d18_inv[i] = N - i;
    for (i = N; i < N2; i++)
      d18_inv[i] = i;
    // decompose permutation cycles
    perm = new Array(N2);
    var p = [ // the permutation
      29,0,32,11,35,20,7,27,2,4,19,28,30,1,5,12,3,9,16,
      22,6,33,8,24,26,21,14,10,34,31,15,25,17,13,23,18
    ], b = new A8(N2); // assert p.length == N2
    i = 0;
    while (i < b.length) {
      var h = [null], c = h, l = 0;
      while (!b[i]) {
        var cc = [null, p[i]];
        c[0] = cc; c = cc;
        b[i] = true;
        i = p[i];
        l++;
      }
      c[0] = h[0];
      for (var j = 0; j < l; j++) {
        var pp = perm[c[1]] = new A8(l);
        for (var k = 0; k < l; k++) {
          pp[k] = c[1];
          c = c[0];
        }
        c = c[0];
      }
      for (i = 0; i < b.length && b[i]; i++) {}
    }
    // set up translation tables
    a2i = new A8(256);
    for (i = 0; i < a2i.length; i++) a2i[i] = NA;
    for (i = 0x30; i < 0x3a; i++) a2i[i] = i - 0x30;
    for (i = 0x41; i < 0x5b; i++) a2i[i] = i - 0x41 + 10;
    for (i = 0x61; i < 0x7b; i++) a2i[i] = i - 0x61 + 10;
    i2a = new A8(N2);
    for (i = 0; i < 10; i++) i2a[i] = i + 0x30;
    for (i = 10; i < N2; i++) i2a[i] = i + 0x41 - 10;
  })();

  // group operation
  var op = function(i, j) {
    return d18_op[N2*i+j];
  }

  // compute n-th application of the permutation
  var nperm = function(i, n) {
    return perm[i][n % perm[i].length];
  }

  // verify correctness of check digit
  var verify = function(str) {
    var i = 0, c = 0, l = str.length;
    while (l--) {
      var ch = a2i[str.charCodeAt(l) & 0xff];
      if (ch != NA)
        c = op(c,nperm(ch,i++));
    }
    return c;
  }

  // Create new check digit
  var create = function(str) {
    var i = 1, c = 0, l = str.length;
    while (l--) {
      var ch = a2i[str.charCodeAt(l) & 0xff];
      if (ch != NA)
        c = op(c,nperm(ch,i++));
    }
    return i2a[d18_inv[c]];
  }

  // Append check digit to given string
  var append = function(str) {
    return str + String.fromCharCode(create(str));
  }

  // export functions
  return {
    'verify': verify,
    'create': create,
    'append': append
  };
}();