| 1 | //! fixed-length fifo sample delay. |
| 2 | |
| 3 | pub struct DelayLine { |
| 4 | buf: Vec<f32>, |
| 5 | write_idx: usize, |
| 6 | } |
| 7 | |
| 8 | impl DelayLine { |
| 9 | /// 0 clamps to 1 (one-sample identity minimum). |
| 10 | #[must_use] |
| 11 | pub fn new(samples: usize) -> Self { |
| 12 | Self { |
| 13 | buf: vec![0.0; samples.max(1)], |
| 14 | write_idx: 0, |
| 15 | } |
| 16 | } |
| 17 | |
| 18 | #[must_use] |
| 19 | pub fn len(&self) -> usize { |
| 20 | self.buf.len() |
| 21 | } |
| 22 | |
| 23 | #[must_use] |
| 24 | pub fn is_empty(&self) -> bool { |
| 25 | false |
| 26 | } |
| 27 | |
| 28 | /// write `x`, return the sample written `len` calls ago. |
| 29 | pub fn push_pop(&mut self, x: f32) -> f32 { |
| 30 | let out = self.buf[self.write_idx]; |
| 31 | self.buf[self.write_idx] = x; |
| 32 | self.write_idx = (self.write_idx + 1) % self.buf.len(); |
| 33 | out |
| 34 | } |
| 35 | |
| 36 | pub fn reset(&mut self) { |
| 37 | for v in &mut self.buf { |
| 38 | *v = 0.0; |
| 39 | } |
| 40 | self.write_idx = 0; |
| 41 | } |
| 42 | } |
| 43 | |
| 44 | #[cfg(test)] |
| 45 | mod tests { |
| 46 | use super::*; |
| 47 | |
| 48 | #[test] |
| 49 | fn delays_exactly_n_samples() { |
| 50 | let mut d = DelayLine::new(4); |
| 51 | let expected = [0.0, 0.0, 0.0, 0.0, 1.0, 2.0, 3.0, 4.0]; |
| 52 | let inputs = [1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0]; |
| 53 | for (i, &x) in inputs.iter().enumerate() { |
| 54 | let y = d.push_pop(x); |
| 55 | assert!((y - expected[i]).abs() < 1e-9, "i={i} y={y}"); |
| 56 | } |
| 57 | } |
| 58 | |
| 59 | #[test] |
| 60 | fn zero_length_clamps_to_one() { |
| 61 | let mut d = DelayLine::new(0); |
| 62 | assert_eq!(d.len(), 1); |
| 63 | assert_eq!(d.push_pop(1.0), 0.0); |
| 64 | assert_eq!(d.push_pop(2.0), 1.0); |
| 65 | } |
| 66 | } |