fn powf_dd<B: PowfBackend>(
idx_x: i32,
dx: f64,
y6: f64,
lo6_hi: f64,
exp2_hi_mid: DoubleDouble,
backend: &B,
) -> f64fn powf_dd<B: PowfBackend>(
idx_x: i32,
dx: f64,
y6: f64,
lo6_hi: f64,
exp2_hi_mid: DoubleDouble,
backend: &B,
) -> f64