nihav-core/src/dsp/window.rs

   1 use std::f32::consts;
   2
   3 #[derive(Debug,Clone,Copy,PartialEq)]
   4 pub enum WindowType {
   5     Square,
   6     Sine,
   7     KaiserBessel(f32),
   8 }
   9
  10 pub fn generate_window(mode: WindowType, scale: f32, size: usize, half: bool, dst: &mut [f32]) {
  11     match mode {
  12         WindowType::Square => {
  13                 for n in 0..size { dst[n] = scale; }
  14             },
  15         WindowType::Sine => {
  16                 let param = if half {
  17                         consts::PI / ((2 * size) as f32)
  18                     } else {
  19                         consts::PI / (size as f32)
  20                     };
  21                 for n in 0..size {
  22                     dst[n] = (((n as f32) + 0.5) * param).sin() * scale;
  23                 }
  24             },
  25         WindowType::KaiserBessel(alpha) => {
  26                 let dlen = if half { size as f32 } else { (size as f32) * 0.5 };
  27                 let alpha2 = f64::from((alpha * consts::PI / dlen) * (alpha * consts::PI / dlen));
  28
  29                 let mut kb: Vec<f64> = Vec::with_capacity(size);
  30                 let mut sum = 0.0;
  31                 for n in 0..size {
  32                     let b = bessel_i0(((n * (size - n)) as f64) * alpha2);
  33                     sum += b;
  34                     kb.push(sum);
  35                 }
  36                 sum += 1.0;
  37                 for n in 0..size {
  38                     dst[n] = (kb[n] / sum).sqrt() as f32;
  39                 }
  40             },
  41     };
  42 }
  43
  44 fn bessel_i0(inval: f64) -> f64 {
  45     let mut val: f64 = 1.0;
  46     for n in (1..64).rev() {
  47         val *= inval / f64::from(n * n);
  48         val += 1.0;
  49     }
  50     val
  51 }