opus-rs 0.1.8

pure Rust implementation of Opus codec
Documentation 
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use crate::pitch::pitch_xcorr;

pub fn lpc(lpc: &mut [f32], ac: &[f32], p: usize) {

    let mut error = ac[0];
    if error <= 1e-10 {
        for x in lpc.iter_mut() {
            *x = 0.0;
        }
        return;
    }

    for i in 0..p {

        let mut rr = 0.0f32;
        for j in 0..i {
            rr += lpc[j] * ac[i - j];
        }
        rr += ac[i + 1];
        let r = -rr / error;

        lpc[i] = r;
        for j in 0..i.div_ceil(2) {
            let tmp1 = lpc[j];
            let tmp2 = lpc[i - 1 - j];
            lpc[j] = tmp1 + r * tmp2;
            lpc[i - 1 - j] = tmp2 + r * tmp1;
        }

        error = error - r * r * error;

        if error <= 0.001 * ac[0] {
            break;
        }
    }
}

pub fn autocorr(
    x: &[f32],
    ac: &mut [f32],
    window: Option<&[f32]>,
    overlap: usize,
    lag: usize,
    n: usize,
) {

    let mut xx = Vec::with_capacity(n);

    if let Some(win) = window {
        if x.len() < n {

            return;
        }

        xx.extend_from_slice(&x[0..n]);
        for i in 0..overlap {
            xx[i] *= win[i];
            xx[n - 1 - i] *= win[i];
        }
    } else {
        xx.extend_from_slice(&x[0..n]);
    }

    let fast_n = n - lag;

    pitch_xcorr(&xx, &xx, ac, fast_n, lag + 1);

    for k in 0..=lag {
        let mut d = 0.0f32;
        for i in (k + fast_n)..n {
            d += xx[i] * xx[i - k];
        }
        ac[k] += d;
    }
}

pub fn celt_fir(x: &[f32], num: &[f32], y: &mut [f32], n: usize, ord: usize) {

    for i in 0..n {
        let mut sum = x[i];
        for j in 0..ord {
            if i > j {
                sum += num[j] * x[i - j - 1];
            }
        }
        y[i] = sum;
    }
}

pub fn celt_iir(x: &[f32], den: &[f32], y: &mut [f32], n: usize, ord: usize, mem: &mut [f32]) {

    for i in 0..n {
        let mut sum = x[i];
        for j in 0..ord {
            sum -= den[j] * mem[j];
        }
        for j in (1..ord).rev() {
            mem[j] = mem[j - 1];
        }
        mem[0] = sum;
        y[i] = sum;
    }
}