Quick Rust algorithm to find prime factors of a number

fac.rs

fn fac(n: u64) -> Vec<u64>
{
    let step = |x| (1 + ((x << 2) as i32) - (((x >> 1) as i32) << 1)) as u64;
    let maxq: u64 = (n as f64).sqrt().floor() as u64;
    let mut d = 1;
    let mut q = if n % 2 == 0 {2} else {3};

    while q <= maxq && n % q != 0
    {
        q = step(d);
        d += 1;
    }

    if q <= maxq 
    {
        let mut v: Vec<u64> = vec![q];
        v.extend(fac(n / q));
        return v;
    } 
    
    else 
    {
        let v: Vec<u64> = vec![n];
        return v;
    }
}