Quick Sort In-place Implementation

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 <?php
 function swap( &$a, &$b )
 {
     $c = $a;
     $a = $b;
     $b = $c;
 }

 /**
 * quick sort
 * ascend
 * in-place
 */
 function quick_sort( &$a )
 {
     $s = count( $a ); // size of a
     if ( $s < 2 ) return;
     $i = 0; // index of pivot, for tracking pivot
     $pivot = $a[$i];
     $l = 0; // swap listener, if listens no swap, sort fini

     // swap those smaller than pivot to the left
     for ( $m = 0; $m < $s; $m++ )
     {
         if ( $a[$m] < $a[$i] )
         {
             swap( $a[$m], $a[$i] );
             $i = $m;
             $l++;
         }
     }

     // swap those larger than pivot to the right
     for ( $n = 0; $n < $i; $n++)
     {
         if ( $a[$n] > $a[$i] )
         {
             swap( $a[$n], $a[$i] );
             $i = $n;
             $l++;
         }
     }

     if ( $l == 0 ) return;
     else $l = 0;
     quick_sort( $a );
 }

 $arr = range( 9, 0 );
 quick_sort( $arr );
 echo implode( ', ', $arr );
 ?>