Calculate the fixed point of cosine in Rust.

rust-cosine-fixedpoint.rs

const TOLERANCE: f64 = 0.00000000000000000001;

fn tolerance_equals(a: f64, b: f64) -> bool {
  ((a - b) * (a - b)) < TOLERANCE
}

fn recursive_cosine_fixedpoint(a: f64) -> f64 {
  if tolerance_equals(a, a.cos()) {
    a
  } else {
    recursive_cosine_fixedpoint(a.cos())
  }
}

fn main() {
  println!("The fixed point of cosine is {}", recursive_cosine_fixedpoint(1f64));
}
// The fixed point of cosine is 0.7390851331706995