Function validate_binary_quadratic_form 

pub(super) fn validate_binary_quadratic_form<U: Limbs>(
    a: NonZero<U>,
    (b_positive, b_abs): (Choice, U),
    discriminant_abs: &U::Wide,
) -> CtOption<(NonZero<U>, (Choice, U), U::Wide)>

Validate a positive definite binary quadratic form (of negative discriminant) as primitive and reduced.

This function runs in constant time.