39 lines
1.1 KiB
Rust
39 lines
1.1 KiB
Rust
use generic_array::{ArrayLength, GenericArray};
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/// Arbitrary order, high dynamic range, wide coefficient range,
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/// lowpass filter implementation.
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///
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/// Type argument N is the filter order + 1.
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#[derive(Clone, Default)]
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pub struct Lowpass<N: ArrayLength<i32>> {
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// IIR state storage
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xy: GenericArray<i32, N>,
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}
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impl<N: ArrayLength<i32>> Lowpass<N> {
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/// Update the filter with a new sample.
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///
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/// # Args
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/// * `x`: Input data
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/// * `k`: Log2 time constant, 1..32
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///
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/// # Return
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/// Filtered output y
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pub fn update(&mut self, x: i32, k: u8) -> i32 {
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debug_assert!((1..32).contains(&k));
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// This is an unrolled and optimized first-order IIR loop
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// that works for all possible time constants.
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// Note the zero(s) at Nyquist.
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let mut x0 = x;
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let mut x1 = self.xy[0];
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self.xy[0] = x0;
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for y1 in self.xy[1..].iter_mut() {
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x0 = *y1
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+ (((x0 >> 2) + (x1 >> 2) - (*y1 >> 1) + (1 << (k - 1))) >> k);
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x1 = *y1;
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*y1 = x0;
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}
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x0
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}
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}
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