Function cme_conversion_factor 

pub fn cme_conversion_factor(
    coupon: f64,
    maturity: NaiveDate,
    delivery_month_start: NaiveDate,
    rounding: CmeMaturityRounding,
) -> f64

The CME Treasury futures conversion factor: the price of $1 of the bond at a 6% yield, a·[(coupon/2) + c + d] − b, rounded to four decimals, as CME’s Calculating U.S. Treasury Futures Conversion Factors defines it.

coupon is the annual coupon as a decimal (0.0375), rounded here to the nearest 1/8% with ties up. Remaining maturity runs in whole months from delivery_month_start (the first day of the delivery month) to maturity (or the call date): n whole years and z further months, z rounded down to a quarter under CmeMaturityRounding::Quarter. Then v = z for z < 7, else z − 6; a = 1.03^(−v/6); b = (coupon/2)(6 − v)/6; c = 1.03^(−2n) for z < 7, else 1.03^(−(2n+1)); d = (coupon/0.06)(1 − c).