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lowpass: robustify

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This commit is contained in:
Robert Jördens 2021-02-10 13:44:10 +01:00
parent 8d68504026
commit beeb43bf8b
1 changed files with 4 additions and 3 deletions
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7
dsp/src/lowpass.rs
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@ -15,19 +15,20 @@ impl<N: ArrayLength<i32>> Lowpass<N> {
/// ///
/// # Args /// # Args
/// * `x`: Input data /// * `x`: Input data
/// * `k`: Log2 time constant /// * `k`: Log2 time constant, 1..32
/// ///
/// # Return /// # Return
/// Filtered output y /// Filtered output y
pub fn update(&mut self, x: i32, k: u8) -> i32 { pub fn update(&mut self, x: i32, k: u8) -> i32 {
debug_assert!((1..32).contains(&k));
// This is an unrolled and optimized first-order IIR loop // This is an unrolled and optimized first-order IIR loop
// that works for all possible time constants. // that works for all possible time constants.
// Note the zero(s) at Nyquist and the benign overflow (DF-I). // Note the zero(s) at Nyquist.
let mut x0 = x; let mut x0 = x;
let mut x1 = self.xy[0]; let mut x1 = self.xy[0];
self.xy[0] = x0; self.xy[0] = x0;
for y1 in self.xy[1..].iter_mut() { for y1 in self.xy[1..].iter_mut() {
x0 = *y1 + (((x0 >> 1) + (x1 >> 1) - *y1 + (1 << (k - 1))) >> k); x0 = *y1 + (((x0 >> 2) + (x1 >> 2) - (*y1 >> 1) + (1 << (k - 1))) >> k);
x1 = *y1; x1 = *y1;
*y1 = x0; *y1 = x0;
} }