function ROTn(text, map) {
  // Generic ROT-n algorithm for keycodes in MAP.
  var R = new String()
  var i, j, c, len = map.length
  for(i = 0; i < text.length; i++) {
    c = text.charAt(i)
    j = map.indexOf(c)
    if (j >= 0) {
      c = map.charAt((j + len / 2) % len)
    }
    R = R + c
  }
  return R;
}

function ROT47(text) {
  // Hides all ASCII-characters from 33 ("!") to 126 ("~").  Hence can be used
  // to obfuscate virtually any text, including URLs and emails.
  var R = new String()
  R = ROTn(text,
  "!\"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`abcdefghijklmnopqrstuvwxyz{|}~")
  return R;
}