#[inline(always)]
pub fn fft2_real(x: [u64; 2]) -> [i64; 2] {
[(x[0] as i64 + x[1] as i64), (x[0] as i64 - x[1] as i64)]
}
#[inline(always)]
pub fn ifft2_real_unreduced(y: [i64; 2]) -> [u64; 2] {
[(y[0] + y[1]) as u64, (y[0] - y[1]) as u64]
}
#[inline(always)]
pub fn fft4_real(x: [u64; 4]) -> (i64, (i64, i64), i64) {
let [z0, z2] = fft2_real([x[0], x[2]]);
let [z1, z3] = fft2_real([x[1], x[3]]);
let y0 = z0 + z1;
let y1 = (z2, -z3);
let y2 = z0 - z1;
(y0, y1, y2)
}
#[inline(always)]
pub fn ifft4_real_unreduced(y: (i64, (i64, i64), i64)) -> [u64; 4] {
let z0 = y.0 + y.2;
let z1 = y.0 - y.2;
let z2 = y.1 .0;
let z3 = -y.1 .1;
let [x0, x2] = ifft2_real_unreduced([z0, z2]);
let [x1, x3] = ifft2_real_unreduced([z1, z3]);
[x0, x1, x2, x3]
}