Something

<?phpfunction hash_part($fp,$start,$length) {        $ctx = hash_init('md5'); 	$ch = "";	$remaining=$length;	$chunkSize=65536;	while ($remaining > 0) {		$data = fread($fp, $chunkSize);				$read = hash_update($ctx, $data);		$ch .= md5sum($data);				$remaining -= strlen($data);        }	        return hash_final($ctx) . " : " . md5sum($ch);}?>