Function rgsl::gamma_beta::gamma::lngamma_sgn_e

pub fn lngamma_sgn_e(x: f64, sgn: &mut f64) -> (Value, Result)

This routine computes the sign of the gamma function and the logarithm of its magnitude, subject to x not being a negative integer or zero. The function is computed using the real Lanczos method. The value of the gamma function and its error can be reconstructed using the relation \Gamma(x) = sgn * \exp(result_lg), taking into account the two components of result_lg.