Function genus2_jacobian_order_general 

pub fn genus2_jacobian_order_general(f: &[BigInt], p: &BigInt) -> i128

#Jac(C)(𝔽_p) for C: y² = f(x) of any degree 5 or 6, with the correct number of points at infinity: deg 5 ⟹ 1; deg 6 ⟹ 2 if the leading coefficient is a square (over 𝔽_p), else 0. Over 𝔽_{p²} every 𝔽_p leading coefficient is a square, so the count there is 2 (deg 6) or 1 (deg 5). Needed to compare a Richelot dual (a non-monic, possibly quadratic-twisted sextic) against its domain.