Function checked_reciprocal_2 

pub fn checked_reciprocal_2(d: u128) -> Option<u64>

Checked version of reciprocal_2_mg10. Returns None if $\mathsf{d} < 2^{127}$.

⚠️ Computes $\floor{\frac{2^{192} - 1}{\mathsf{d}}} - 2^{64}$.

⚠️ This function is not part of the stable API.