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;
  17                 if half {
  18                     param = consts::PI / ((2 * size) as f32);
  19                 } else {
  20                     param = consts::PI / (size as f32);
  21                 }
  22                 for n in 0..size {
  23                     dst[n] = (((n as f32) + 0.5) * param).sin() * scale;
  24                 }
  25             },
  26         WindowType::KaiserBessel(alpha) => {
  27                 let dlen = if half { size as f32 } else { (size as f32) * 0.5 };
  28                 let alpha2 = ((alpha * consts::PI / dlen) * (alpha * consts::PI / dlen)) as f64;
  29
  30                 let mut kb: Vec<f64> = Vec::with_capacity(size);
  31                 let mut sum = 0.0;
  32                 for n in 0..size {
  33                     let b = bessel_i0(((n * (size - n)) as f64) * alpha2);
  34                     sum += b;
  35                     kb.push(sum);
  36                 }
  37                 sum += 1.0;
  38                 for n in 0..size {
  39                     dst[n] = (kb[n] / sum).sqrt() as f32;
  40                 }
  41             },
  42     };
  43 }
  44
  45 fn bessel_i0(inval: f64) -> f64 {
  46     let mut val: f64 = 1.0;
  47     for n in (1..64).rev() {
  48         val *= inval / ((n * n) as f64);
  49         val += 1.0;
  50     }
  51     val
  52 }