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lib.rs
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lib.rs
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//! # cic-fixed
//!
//! A CIC filter implementation for fixed point numbers.
//! Implemented for use in converting PDM to PCM.
//!
//! ## Example
//!
//! ```rust
//! use cic_fixed::CicDecimationFilter;
//!
//! let mut filter = CicDecimationFilter::<4, 2>::new();
//! let result = filter.filter(0);
//! assert!(result.is_none());
//! let result = filter.filter(1);
//! assert!(result.is_none());
//! let result = filter.filter(2);
//! assert!(result.is_none());
//! let result = filter.filter(3);
//! assert!(result.is_some());
//! assert_eq!(result.unwrap(), 10);
//! ```
//!
#![cfg_attr(not(test), no_std)]
mod decimator;
mod differentiator;
mod integrator;
/// CIC decimation filter.
/// - `M` - Decimation factor
/// - `N` - Number of stages
pub struct CicDecimationFilter<const M: usize, const N: usize> {
decimator: decimator::Decimator<M>,
integrators: [integrator::Integrator; N],
differentiators: [differentiator::Differentiator; N],
}
impl<const M: usize, const N: usize> CicDecimationFilter<M, N> {
pub const fn new() -> Self {
assert!(M > 0, "M (decimation factor) must be greater than 0. Without decimation, the CIC filter does not perform as an LPF.");
assert!(N > 0, "N (number of stages) must be greater than 0");
Self {
decimator: decimator::Decimator::new(),
integrators: [integrator::Integrator::new(); N],
differentiators: [differentiator::Differentiator::new(); N],
}
}
/// Process the input and return the output when the decimator is ready to output a value.
///
/// # Arguments
///
/// * `input` - The input to filter.
///
/// # Returns
///
/// The output of the filter.
/// The output range is Input range * (M^N). For example, if Input range is +/-1, M is 4, and N is 2, the output range is +/-16.
/// When the decimator is ready to output a value, it will return some(input). Otherwise, it will return None.
#[inline]
#[must_use]
pub fn filter(&mut self, input: i32) -> Option<i32> {
let mut output = input;
for integrator in self.integrators.iter_mut() {
output = integrator.integrate(output);
}
if let Some(output) = self.decimator.decimate(output) {
let mut v = output;
for differentiator in self.differentiators.iter_mut() {
v = differentiator.differentiate(v);
}
Some(v)
} else {
None
}
}
/// Returns the number of bits increased by passing through the CIC deciamtion filter.
/// The bit increase by the CIC decimation filter can be expressed by the following equation.
/// log2(M)*N
/// M is the decimation factor and N is the number of stages.
#[must_use]
pub const fn bit_growth(&self) -> u32 {
M.ilog2() * N as u32
}
}
impl<const M: usize, const N: usize> Default for CicDecimationFilter<M, N> {
fn default() -> Self {
Self::new()
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn cic_decimation_test() {
let mut filter = CicDecimationFilter::<4, 2>::new();
let result = filter.filter(0);
assert!(result.is_none());
let result = filter.filter(1);
assert!(result.is_none());
let result = filter.filter(2);
assert!(result.is_none());
let result = filter.filter(3);
assert!(result.is_some());
assert_eq!(result.unwrap(), 10);
let result = filter.filter(2);
assert!(result.is_none());
let result = filter.filter(-1);
assert!(result.is_none());
let result = filter.filter(-2);
assert!(result.is_none());
let result = filter.filter(1);
assert!(result.is_some());
assert_eq!(result.unwrap(), 16);
let result = filter.filter(2);
assert!(result.is_none());
let result = filter.filter(-1);
assert!(result.is_none());
let result = filter.filter(-2);
assert!(result.is_none());
let result = filter.filter(1);
assert!(result.is_some());
assert_eq!(result.unwrap(), 0);
let result = filter.filter(2);
assert!(result.is_none());
let result = filter.filter(-1);
assert!(result.is_none());
let result = filter.filter(-2);
assert!(result.is_none());
let result = filter.filter(1);
assert!(result.is_some());
assert_eq!(result.unwrap(), 0);
let result = filter.filter(0);
assert!(result.is_none());
let result = filter.filter(1);
assert!(result.is_none());
let result = filter.filter(2);
assert!(result.is_none());
let result = filter.filter(3);
assert!(result.is_some());
assert_eq!(result.unwrap(), 8);
let result = filter.filter(3);
assert!(result.is_none());
let result = filter.filter(3);
assert!(result.is_none());
let result = filter.filter(-2);
assert!(result.is_none());
let result = filter.filter(1);
assert!(result.is_some());
assert_eq!(result.unwrap(), 32);
}
#[test]
fn overflow_test() {
let mut filter = CicDecimationFilter::<4, 2>::new();
for _ in 0..1000 {
filter.filter(i32::MAX);
}
}
// 出力範囲のテスト
// CICフィルターはMが4, Nが2とする。
// 最大出力はM^N = 4^2 = 16倍される。
// 入力範囲が-1~1の場合、出力範囲は-16~16
#[test]
fn output_range_test() {
let mut filter = CicDecimationFilter::<4, 2>::new();
for _ in 0..1000 {
let _result = filter.filter(1);
}
for _ in 0..10 {
if let Some(output) = filter.filter(1) {
println!("{}", output);
assert!(output == 16); //4^2
}
}
for _ in 0..1000 {
let _result = filter.filter(-1);
}
for _ in 0..10 {
if let Some(output) = filter.filter(-1) {
println!("{}", output);
assert!(output == -16); //4^2
}
}
}
#[test]
fn bit_growth_test() {
let filter = CicDecimationFilter::<64, 3>::new();
assert_eq!(filter.bit_growth(), 18);
let filter = CicDecimationFilter::<32, 5>::new();
assert_eq!(filter.bit_growth(), 25);
let filter = CicDecimationFilter::<8, 5>::new();
assert_eq!(filter.bit_growth(), 15);
}
}