Auto update copyright in footer with error protection

AutoCopyrightUpdate.php

<!--Referenced from https://css-tricks.com/snippets/php/automatic-copyright-year/-->

<!--Start date with error protection-->
<?php function auto_copyright($year = 'auto'){ ?>
   <?php if(intval($year) == 'auto'){ $year = date('Y'); } ?>
   <?php if(intval($year) == date('Y')){ echo intval($year); } ?>
   <?php if(intval($year) < date('Y')){ echo intval($year) . ' - ' . date('Y'); } ?>
   <?php if(intval($year) > date('Y')){ echo date('Y'); } ?>
<?php } ?>

<!--Usage-->
<?php auto_copyright('2009');  // 2009 - 2015 ?>