PHP - Calculate pi

From Global Programming Syntax

Pi is a never ending number unless you use an inaccurate formula. Below is an example of a php script to calculate pi using Vieta's Pi Formula. To use this script, it will take at least 3 minutes to get a decent result of pi for the below script and if you are not worried about cpu usage then you can remove the 2 lines with the sleep functions for much faster performance. You will find when using this script, it will keep on re-displaying pi but each time pi is redisplayed, it will usually append a digit or two.

<?
set_time_limit(0);
echo str_repeat('    ', 64).'<br>';
$digits=600;
$pival='1';
$str1='';
while ($pirow<2000)
    {
    $pirow+=1;
    $tempval='0';
    for ($pisubrow=0;$pisubrow<$pirow;$pisubrow++)
        {
        $tempval=bcsqrt(bcadd('2',$tempval,$digits),$digits);
        if (($pisubrow/2)==round($pisubrow/2)) { sleep(1); }
        }
    $tempval=bcdiv('2',$tempval,$digits);
    $pival=bcmul($tempval,$pival,$digits);
    unset($tempval);      
    $tempval=bcmul('2',$pival,$digits);
    $common = array();
    $length = (strlen($str1) >= strlen($tempval)) ? strlen($str1) : strlen($tempval);
    for($x=0;$x<$length;$x++){
        if($str1[$x] == $tempval[$x]){
            $common[] = $str1[$x]; 
        }else{
            break;
        }
    }
    if ($pirow>5)
        {
        echo 'pi='.substr(join('',$common),0,-2).'<p>';
        }
    unset($str1);
    $str1=$tempval;    
    unset($tempval);
    flush();
    sleep(1);
    }
$pival=bcmul($pival,'2',$digits);
unset($pirow);
?>

The first 490 digits are: 3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679
82148086513282306647093844609550582231725359408128481117450284102701938521105559644622948954930381964428810975665933446
12847564823378678316527120190914564856692346034861045432664821339360726024914127372458700660631558817488152092096282925
40917153643678925903600113305305488204665213841469519415116094330572703657595919530921861173819326117931051185480744623
799627495673518857527248912279