var isNN = (navigator.appName.indexOf('Netscape') != -1);

function autoTab(input, len, e)
{
   var keyCode = isNN ? e.which : e.keyCode;
   var filter = isNN ? [0,8,9] : [0,8,9,16,17,18,37,38,39,40,46];

   if (input.value.length >= len && !containsElement(filter, keyCode))
   {
      input.value = input.value.slice(0, len);
      input.form[(getIndex(input) + 1) % input.form.length].focus();
   }

   return true;
}

function containsElement(arr, ele)
{
   var found = false, index = 0;

   while(!found && index < arr.length)
      if (arr[index] == ele)
         found = true;
      else
         index++;

   return found;
}
   
function getIndex(input)
{
   var index = -1, i = 0, found = false;

   while (i < input.form.length && index == -1)
      if (input.form[i] == input)
         index = i;
      else
         i++;

   return index;
}