Difference between two stardates

<?php
    /*
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    94305, USA.
    */
 
	// Calculate the difference between two stardates.
	function stardatediff($firstStardate, $secondStardate)
	{
        $years1 = substr($firstStardate, 0, 2);
        $years2 = substr($secondStardate, 0, 2);
 
        $days1 = substr($firstStardate, 2, 3);
        $days2 = substr($secondStardate, 2, 3);
 
        $hours1 = substr($firstStardate, 6, 1);
        $hours2 = substr($secondStardate, 6, 1);
 
        if ($years1 > $years2)
        {
            $years = $years1 - $years2;
        }
        else
        {
            $years = $years2 - $years1;
        }
 
        if ($days1 > $days2)
        {
            $days = ($days1 * 366 / 1000) - ($days2 * 366 / 1000);
        }
        else
        {
            $days = ($days2 * 366 / 1000) - ($days1 * 366 / 1000);
        }
 
        if ($hours1 > $hours2)
        {
            $hours = ($hours1 * 144 / 60) - ($hours2 * 144 / 60);
        }
        else
        {
            $hours = ($hours2 * 144 / 60) - ($hours1 * 144 / 60);
        }
 
        $days = round($days);
        $hours = round($hours, 1);
 
        return "There are $years years, $days days, and $hours hours between Stardate $firstStardate and Stardate $secondStardate.";
	}
?>