pidigits800.v

// This program is a direct port of https://crypto.stanford.edu/pbc/notes/pi/code.html
// which in turn is an implementation of (Beeler et al. 1972, Item 120),
// see https://mathworld.wolfram.com/PiFormulas.html
// It calculates and prints the first 800 digits of pi, using only integer math.
const maxr = 2800

fn main() {
	mut r := [maxr + 1]int{}
	mut i, mut k, mut b, mut d, mut c := 0, 0, 0, 0, 0
	for i = 0; i < maxr; i++ {
		r[i] = 2000
	}
	for k = maxr; k > 0; k -= 14 {
		d = 0
		i = k
		for {
			d += r[i] * 10000
			b = 2 * i - 1
			r[i] = d % b
			d /= b
			i--
			if i == 0 {
				break
			}
			d *= i
		}
		print('${c + d / 10000:04d}')
		c = d % 10000
	}
}