get pi with fib

pi.rs

use std::f64;
fn rnd10(f: f64) -> f64 { (f * 1e10).round() / 1e10 }

fn iter_pi(epsilon: f64) -> (i32, f64) {
    let mut x = 0.0;
    let mut fib = vec![0, 1];
    let mut cnt = 0;
    loop {
        if cnt >= 1 {
            let n = fib[2 * cnt - 2] + fib[2 * cnt - 1];
            fib.push(n);
            let n = fib[2 * cnt] + fib[2 * cnt - 1];
            fib.push(n);
        }
        x += 4. * (1.0 / fib[2 * cnt + 1] as f64).atan();
        println!("{}", x);
        if (x - f64::consts::PI).abs() < epsilon {
            return ((cnt + 1) as i32, x);
        }
        cnt += 1;
    }
}