<?php
function djbx33a($key, $len) {
  $hash = 5381;
  for($i=0; $i < $len; $i++) {
    $hash = $hash * 33 + chr($key[$i]);
  }
  return $hash . "<br>\n";
}

echo djbx33a('1024',4);
echo djbx33a('2048',4);
echo djbx33a('3072',4);