global values

[lattice0]

Iḿ struggling with performance because rust has no globlal variables and thus I have to parse them all the time in the code. Using lazy_static actually introduces some overhead. How to have fast constants for usage in code?

pub fn ln_halley(x: &BigDecimal, scale: i64) -> BigDecimal {
    //parsing this everytime is bad
    let epsilon = BigDecimal::from_f64(0.00000000000000001).unwrap();
    let mut y = x - &BigDecimal::one();
    let y_0 = y.clone();
    loop {
        //parsing "2" all the time here too
        y = &y + BigDecimal::from_u64(2).unwrap()*(x-&y.exp())/(x+y.exp());
        if (&y-&y_0).abs() < epsilon {
            break;
        }
    }
    y
}