I wrote this function with many BCMath functions. It should be the fastest function in PHP to find the number pi into any precision, my test is it generate 2000 digits after the dot in 8 seconds. I don't think you need anything more than that.
<?php
function bcpi($precision){
$limit = ceil(log($precision)/log(2))-1;
bcscale($precision+6);
$a = 1;
$b = bcdiv(1,bcsqrt(2));
$t = 1/4;
$p = 1;
while($n < $limit){
$x = bcdiv(bcadd($a,$b),2);
$y = bcsqrt(bcmul($a, $b));
$t = bcsub($t, bcmul($p,bcpow(bcsub($a,$x),2)));
$a = $x;
$b = $y;
$p = bcmul(2,$p);
++$n;
}
return bcdiv(bcpow(bcadd($a, $b),2),bcmul(4,$t),$precision);
}
?>
