Versions of calculating PI (where [x] ≒ [PI])

calcpi.js

console.clear();
console.log('[Start]');

sqrt = Math.sqrt;

a = n = 1;
g = 1 / sqrt(2); z = 1 / 4; half = 1 / 2;

for(var i = 0; i < 30; i++) {
  x = [(a + g) * half, sqrt(a * g)];
  val = x[0] - a;
  z -= val * val * n;
  n += n;
  a = x[0]; g = x[1];
}
console.log(a * a / z);
console.log('[End]');
// Failure - 15 point decimal rounding