use std::f32::consts;
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum WindowType {
Sine,
KaiserBessel(f32),
}
pub fn generate_window(mode: WindowType, scale: f32, size: usize, half: bool, dst: &mut [f32]) {
match mode {
WindowType::Sine => {
let param =
if half { consts::PI / ((2 * size) as f32) } else { consts::PI / (size as f32) };
for n in 0..size {
dst[n] = (((n as f32) + 0.5) * param).sin() * scale;
}
}
WindowType::KaiserBessel(alpha) => {
let dlen = if half { size as f32 } else { (size as f32) * 0.5 };
let alpha2 = f64::from((alpha * consts::PI / dlen) * (alpha * consts::PI / dlen));
let mut kb: Vec<f64> = Vec::with_capacity(size);
let mut sum = 0.0;
for n in 0..size {
let b = bessel_i0(((n * (size - n)) as f64) * alpha2);
sum += b;
kb.push(sum);
}
sum += 1.0;
for n in 0..size {
dst[n] = (kb[n] / sum).sqrt() as f32;
}
}
};
}
fn bessel_i0(inval: f64) -> f64 {
let mut val: f64 = 1.0;
for n in (1..64).rev() {
val *= inval / f64::from(n * n);
val += 1.0;
}
val
}