Quick sort for associative arrays

<?php
function qsort($a,$f) {
       qsort_do(&$a,0,Count($a)-1,$f);
}

function qsort_do($a,$l,$r,$f) {
       if ($l < $r) {
               qsort_partition(&$a,$l,$r,&$lp,&$rp,$f);
               qsort_do(&$a,$l,$lp,$f);
               qsort_do(&$a,$rp,$r,$f);
       }
}

function qsort_partition($a,$l,$r,$lp,$rp,$f) {
       $i = $l+1;
       $j = $l+1;
       
       while ($j <= $r) {
               if ($f($a[$j],$a[$l])) {
                       $tmp = $a[$j];
                       $a[$j] = $a[$i];
                       $a[$i] = $tmp;
                       $i++;
               }
               $j++;
       }
       
       $x = $a[$l];
       $a[$l] = $a[$i-1];
       $a[$i-1] = $x;
       
       $lp = $i - 2;
       $rp = $i;
}

?>