Javascript function to PHP

[hatching]

How do you change the javascript function into PHP? A local community website has a javascript function placed inside their website from a previous coder and wanted it to be server side. I apologize in advanced if I created this thread under the wrong category.

<script type="text/javascript">
    function dF(s, n) {
        n = parseInt(n);
        var s1 = unescape(s.substr(0, n) + s.substr(n + 1, s.length - n - 1));
        var t = '';
        for (i = 0; i < s1.length; i++) t += String.fromCharCode(s1.charCodeAt(i) - s.substr(n, 1));
        return (unescape(t));
    }

//input
alert(dF('%3Ai64f3iheh9ih38f%3Ag63e4383h7fg%3B353', 15));

//output - 7f31c0febe6fe5c7d30b1050e4cd8020
</script>

[wyattstorch42]

<?php
 function dF($s, $n)
 {
  $s1 = urldecode(substr($s, 0, $n).substr($s, n+1, strlen($s)-$n-1));
  $t = "";
  for($i = 0; $i < strlen($s1); $i++)
   $t += chr(ord(substr($s1, $i, 1)) - substr($s, $n, 1));
  return urldecode($t);
 }
?>

(Untested. Let me know if that works out.)

[hatching]

Thanks for your input wyatt. The converted function wasn't able to send the correct output.