fn sincpi_dd<B: SinCosPiBackend>(
x: f64,
sin_k: DoubleDouble,
cos_k: DoubleDouble,
scale: DoubleDouble,
backend: &B,
) -> f64fn sincpi_dd<B: SinCosPiBackend>(
x: f64,
sin_k: DoubleDouble,
cos_k: DoubleDouble,
scale: DoubleDouble,
backend: &B,
) -> f64