Function carlson_rf 

pub fn carlson_rf<P, E, V>(x: V, y: V, z: V) -> V
where
    P: Policy,
    E: FloatElement + EllipticConsts,
    V: FloatVector<Element = E>,

Carlson symmetric integral of the first kind, R_F(x, y, z), via the duplication algorithm. All Boost special cases are omitted: the duplication converges for any valid input (e.g. a single zero argument becomes positive after one step), so the loop runs uniformly across lanes and stops once every lane has converged.

Two or more zero arguments is the one exception. R_F diverges there, and the duplication only walks toward the pole, so it is pinned to infinity under check_overflow.