mousiki 0.2.1

#![allow(dead_code)]

//! Helpers ported from `celt/celt.c`.
//!
//! This module starts translating small pieces of the CELT top-level glue. The
//! helpers exposed here have no dependencies on the rest of the encoder or
//! decoder state so they can be exercised in isolation while larger control
//! flow is still being translated.

#[cfg(feature = "fixed_point")]
use crate::celt::fixed_arch::{Q15_ONE, SIG_SAT};
#[cfg(feature = "fixed_point")]
use crate::celt::fixed_ops::{add32, mult16_16_p15, mult16_16_q15, mult16_32_q15, sub32};
use crate::celt::math::mul_add_f32;
use crate::celt::types::{CeltCoef, OpusCustomMode, OpusInt32, OpusVal16, OpusVal32};
#[cfg(feature = "fixed_point")]
use crate::celt::types::{FixedCeltCoef, FixedCeltSig, FixedOpusVal16};

/// Minimum comb-filter period supported by the scalar implementation.
pub(crate) const COMBFILTER_MINPERIOD: usize = 15;

/// Tapset gains mirroring the tables embedded in the reference implementation.
const TAPSET_GAINS: [[OpusVal16; 3]; 3] = [
    [0.306_640_62, 0.217_041_02, 0.129_638_67],
    [0.463_867_2, 0.268_066_4, 0.0],
    [0.799_804_7, 0.100_097_656, 0.0],
];

/// Tapset gains for the fixed-point comb filter (Q15).
#[cfg(feature = "fixed_point")]
const TAPSET_GAINS_FIXED: [[FixedOpusVal16; 3]; 3] =
    [[10048, 7112, 4248], [15200, 8784, 0], [26208, 3280, 0]];

/// TF change table mirroring `tf_select_table` from `celt/celt.c`.
///
/// Positive values indicate better frequency resolution (longer effective
/// windows) whereas negative values favour time resolution. The second index is
/// computed as `4 * is_transient + 2 * tf_select + per_band_flag`.
pub(crate) const TF_SELECT_TABLE: [[i8; 8]; 4] = [
    [0, -1, 0, -1, 0, -1, 0, -1],
    [0, -1, 0, -2, 1, 0, 1, -1],
    [0, -2, 0, -3, 2, 0, 1, -1],
    [0, -2, 0, -3, 3, 0, 1, -1],
];

/// Returns the canonical error string associated with an Opus/CELT error code.
///
/// Mirrors `opus_strerror()` from `celt/celt.c` for the subset of error codes
/// used by the reference implementation. Unrecognised codes fall back to the
/// "unknown error" string just like the C helper.
#[must_use]
pub(crate) fn opus_strerror(error: i32) -> &'static str {
    match error {
        0 => "success",
        -1 => "invalid argument",
        -2 => "buffer too small",
        -3 => "internal error",
        -4 => "corrupted stream",
        -5 => "request not implemented",
        -6 => "invalid state",
        -7 => "memory allocation failed",
        _ => "unknown error",
    }
}

/// Compile-time version string matching the format returned by the reference
/// implementation's `opus_get_version_string()` helper.
pub(crate) const OPUS_VERSION_STRING: &str = concat!("libopus ", env!("CARGO_PKG_VERSION"));

/// Returns the textual version identifier for the library.
#[must_use]
pub(crate) fn opus_get_version_string() -> &'static str {
    OPUS_VERSION_STRING
}

/// Applies the constant-coefficient comb filter used by the encoder/decoder.
///
/// Mirrors `comb_filter_const_c()` from `celt/celt.c` for the float build. The
/// `x` slice must expose at least `t + 2` samples of history before
/// `x_start` alongside `y.len()` samples starting at `x_start`, allowing the
/// routine to mirror the negative pointer indexing present in the C
/// implementation.
pub(crate) fn comb_filter_const(
    y: &mut [OpusVal32],
    x: &[OpusVal32],
    x_start: usize,
    t: usize,
    g10: CeltCoef,
    g11: CeltCoef,
    g12: CeltCoef,
) {
    let n = y.len();
    if n == 0 {
        return;
    }

    assert!(t >= COMBFILTER_MINPERIOD, "comb filter period too small");
    assert!(
        x_start >= t + 2,
        "input slice does not provide enough history for the comb filter",
    );
    assert!(
        x.len() >= x_start + n,
        "input slice must provide x_start + n samples",
    );

    let mut x4 = x[x_start - t - 2];
    let mut x3 = x[x_start - t - 1];
    let mut x2 = x[x_start - t];
    let mut x1 = x[x_start - t + 1];

    for (i, sample) in y.iter_mut().enumerate() {
        let current = x[x_start + i];
        let x0 = x[x_start + i - t + 2];
        let mut acc = mul_add_f32(g10, x2, current);
        acc = mul_add_f32(g11, x1 + x3, acc);
        acc = mul_add_f32(g12, x0 + x4, acc);
        *sample = acc;

        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }
}

/// Applies the constant-coefficient comb filter directly within one channel.
///
/// The decoder post-filter reads predictor history and writes the filtered
/// samples back into the same decode buffer. Exposing that shape directly keeps
/// the aliasing semantics in one place and lets hot decode paths stay safe
/// without rebuilding shared raw slices at each call site.
pub(crate) fn comb_filter_const_in_place(
    channel: &mut [OpusVal32],
    output_start: usize,
    n: usize,
    t: usize,
    g10: CeltCoef,
    g11: CeltCoef,
    g12: CeltCoef,
) {
    if n == 0 {
        return;
    }

    assert!(t >= COMBFILTER_MINPERIOD, "comb filter period too small");
    assert!(
        output_start >= t + 2,
        "channel does not provide enough history for the comb filter",
    );
    assert!(
        channel.len() >= output_start + n,
        "channel must provide output_start + n samples",
    );

    let mut x4 = channel[output_start - t - 2];
    let mut x3 = channel[output_start - t - 1];
    let mut x2 = channel[output_start - t];
    let mut x1 = channel[output_start - t + 1];

    for i in 0..n {
        let current = channel[output_start + i];
        let x0 = channel[output_start + i - t + 2];
        let mut acc = mul_add_f32(g10, x2, current);
        acc = mul_add_f32(g11, x1 + x3, acc);
        acc = mul_add_f32(g12, x0 + x4, acc);
        channel[output_start + i] = acc;

        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }
}

#[inline]
fn slices_overlap<T>(lhs: &[T], rhs: &[T]) -> bool {
    if lhs.is_empty() || rhs.is_empty() {
        return false;
    }

    let elem_size = core::mem::size_of::<T>();
    if elem_size == 0 {
        return false;
    }

    let lhs_start = lhs.as_ptr() as usize;
    let rhs_start = rhs.as_ptr() as usize;
    let lhs_end = lhs_start + lhs.len() * elem_size;
    let rhs_end = rhs_start + rhs.len() * elem_size;

    lhs_start < rhs_end && rhs_start < lhs_end
}

/// Applies the out-of-place variable tapset comb filter with optional overlap
/// ramping.
///
/// Mirrors the scalar implementation of `comb_filter()` from `celt/celt.c`.
/// The caller must provide the `x` buffer with enough history before
/// `x_start` (at least `max(T0, T1) + 2` samples) in addition to the `n`
/// samples of the current frame. `y` must provide room for `n` output samples.
/// Callers that need same-buffer updates must use [`comb_filter_in_place`];
/// this out-of-place variant assumes its input and output spans do not overlap.
#[allow(clippy::too_many_arguments)]
pub(crate) fn comb_filter(
    y: &mut [OpusVal32],
    x: &[OpusVal32],
    x_start: usize,
    n: usize,
    mut t0: i32,
    mut t1: i32,
    g0: OpusVal16,
    g1: OpusVal16,
    tapset0: usize,
    tapset1: usize,
    window: &[CeltCoef],
    overlap: usize,
    _arch: i32,
) {
    if n == 0 {
        return;
    }

    assert!(n <= y.len(), "output slice must hold n samples");
    assert!(x.len() >= x_start + n, "input slice must expose n samples");
    assert!(tapset0 < TAPSET_GAINS.len(), "invalid tapset index");
    assert!(tapset1 < TAPSET_GAINS.len(), "invalid tapset index");

    if g0 == 0.0 && g1 == 0.0 {
        let src = &x[x_start..x_start + n];
        let dst = &mut y[..n];
        debug_assert!(
            !slices_overlap(src, dst),
            "comb_filter requires distinct input/output slices; use comb_filter_in_place for overlap",
        );
        dst.copy_from_slice(src);
        return;
    }

    t0 = t0.max(COMBFILTER_MINPERIOD as i32);
    t1 = t1.max(COMBFILTER_MINPERIOD as i32);
    let t0 = t0 as usize;
    let t1 = t1 as usize;

    assert!(
        x_start >= t0 + 2 && x_start >= t1 + 2,
        "input slice lacks the required comb filter history",
    );

    let tap0 = TAPSET_GAINS[tapset0];
    let tap1 = TAPSET_GAINS[tapset1];
    let g00 = g0 * tap0[0];
    let g01 = g0 * tap0[1];
    let g02 = g0 * tap0[2];
    let g10 = g1 * tap1[0];
    let g11 = g1 * tap1[1];
    let g12 = g1 * tap1[2];

    let mut x1 = x[x_start - t1 + 1];
    let mut x2 = x[x_start - t1];
    let mut x3 = x[x_start - t1 - 1];
    let mut x4 = x[x_start - t1 - 2];

    let mut overlap = overlap.min(n);
    if g0 == g1 && t0 == t1 && tapset0 == tapset1 {
        overlap = 0;
    } else if overlap > 0 {
        assert!(
            window.len() >= overlap,
            "window must expose at least overlap samples",
        );
    }

    for i in 0..overlap {
        let x0 = x[x_start + i - t1 + 2];
        let f = window[i] * window[i];
        let one_minus_f = 1.0 - f;

        let current = x[x_start + i];
        let past0 = x[x_start + i - t0];
        let past1 = x[x_start + i - t0 + 1];
        let pastm1 = x[x_start + i - t0 - 1];
        let past2 = x[x_start + i - t0 + 2];
        let pastm2 = x[x_start + i - t0 - 2];

        let g00f = one_minus_f * g00;
        let g01f = one_minus_f * g01;
        let g02f = one_minus_f * g02;
        let g10f = f * g10;
        let g11f = f * g11;
        let g12f = f * g12;

        let mut acc = mul_add_f32(g00f, past0, current);
        acc = mul_add_f32(g01f, past1 + pastm1, acc);
        acc = mul_add_f32(g02f, past2 + pastm2, acc);
        acc = mul_add_f32(g10f, x2, acc);
        acc = mul_add_f32(g11f, x1 + x3, acc);
        acc = mul_add_f32(g12f, x0 + x4, acc);
        y[i] = acc;

        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }

    if g1 == 0.0 {
        if overlap < n {
            let src = &x[x_start + overlap..x_start + n];
            let dst = &mut y[overlap..n];
            debug_assert!(
                !slices_overlap(src, dst),
                "comb_filter requires distinct input/output slices; use comb_filter_in_place for overlap",
            );
            dst.copy_from_slice(src);
        }
        return;
    }

    if overlap < n {
        comb_filter_const(&mut y[overlap..n], x, x_start + overlap, t1, g10, g11, g12);
    }
}

/// Applies the variable tapset comb filter directly within one channel.
///
/// This is the in-place counterpart to [`comb_filter`]. It exists so decode
/// paths that naturally update `decode_mem` in place can express that intent
/// safely and keep the aliasing behaviour local to the filter implementation
/// instead of reconstituting shared input/output slices with `unsafe`.
#[allow(clippy::too_many_arguments)]
pub(crate) fn comb_filter_in_place(
    channel: &mut [OpusVal32],
    output_start: usize,
    n: usize,
    mut t0: i32,
    mut t1: i32,
    g0: OpusVal16,
    g1: OpusVal16,
    tapset0: usize,
    tapset1: usize,
    window: &[CeltCoef],
    overlap: usize,
    _arch: i32,
) {
    if n == 0 {
        return;
    }

    assert!(
        channel.len() >= output_start + n,
        "channel must expose the requested output span",
    );
    assert!(tapset0 < TAPSET_GAINS.len(), "invalid tapset index");
    assert!(tapset1 < TAPSET_GAINS.len(), "invalid tapset index");

    if g0 == 0.0 && g1 == 0.0 {
        return;
    }

    t0 = t0.max(COMBFILTER_MINPERIOD as i32);
    t1 = t1.max(COMBFILTER_MINPERIOD as i32);
    let t0 = t0 as usize;
    let t1 = t1 as usize;

    assert!(
        output_start >= t0 + 2 && output_start >= t1 + 2,
        "channel lacks the required comb filter history",
    );

    let tap0 = TAPSET_GAINS[tapset0];
    let tap1 = TAPSET_GAINS[tapset1];
    let g00 = g0 * tap0[0];
    let g01 = g0 * tap0[1];
    let g02 = g0 * tap0[2];
    let g10 = g1 * tap1[0];
    let g11 = g1 * tap1[1];
    let g12 = g1 * tap1[2];

    let mut x1 = channel[output_start - t1 + 1];
    let mut x2 = channel[output_start - t1];
    let mut x3 = channel[output_start - t1 - 1];
    let mut x4 = channel[output_start - t1 - 2];

    let mut overlap = overlap.min(n);
    if g0 == g1 && t0 == t1 && tapset0 == tapset1 {
        overlap = 0;
    } else if overlap > 0 {
        assert!(
            window.len() >= overlap,
            "window must expose at least overlap samples",
        );
    }

    for i in 0..overlap {
        let x0 = channel[output_start + i - t1 + 2];
        let f = window[i] * window[i];
        let one_minus_f = 1.0 - f;

        let current = channel[output_start + i];
        let past0 = channel[output_start + i - t0];
        let past1 = channel[output_start + i - t0 + 1];
        let pastm1 = channel[output_start + i - t0 - 1];
        let past2 = channel[output_start + i - t0 + 2];
        let pastm2 = channel[output_start + i - t0 - 2];

        let g00f = one_minus_f * g00;
        let g01f = one_minus_f * g01;
        let g02f = one_minus_f * g02;
        let g10f = f * g10;
        let g11f = f * g11;
        let g12f = f * g12;

        let mut acc = mul_add_f32(g00f, past0, current);
        acc = mul_add_f32(g01f, past1 + pastm1, acc);
        acc = mul_add_f32(g02f, past2 + pastm2, acc);
        acc = mul_add_f32(g10f, x2, acc);
        acc = mul_add_f32(g11f, x1 + x3, acc);
        acc = mul_add_f32(g12f, x0 + x4, acc);
        channel[output_start + i] = acc;

        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }

    if g1 == 0.0 {
        return;
    }

    if overlap < n {
        comb_filter_const_in_place(
            channel,
            output_start + overlap,
            n - overlap,
            t1,
            g10,
            g11,
            g12,
        );
    }
}

#[cfg(feature = "fixed_point")]
fn saturate_sig(value: FixedCeltSig) -> FixedCeltSig {
    if value > SIG_SAT {
        SIG_SAT
    } else if value < -SIG_SAT {
        -SIG_SAT
    } else {
        value
    }
}

/// Fixed-point constant-coefficient comb filter.
#[cfg(feature = "fixed_point")]
pub(crate) fn comb_filter_const_fixed(
    y: &mut [FixedCeltSig],
    x: &[FixedCeltSig],
    x_start: usize,
    t: usize,
    g10: FixedOpusVal16,
    g11: FixedOpusVal16,
    g12: FixedOpusVal16,
) {
    let n = y.len();
    if n == 0 {
        return;
    }

    assert!(t >= COMBFILTER_MINPERIOD, "comb filter period too small");
    assert!(
        x_start >= t + 2,
        "input slice does not provide enough history for the comb filter",
    );
    assert!(
        x.len() >= x_start + n,
        "input slice must provide x_start + n samples",
    );

    let mut x4 = x[x_start - t - 2];
    let mut x3 = x[x_start - t - 1];
    let mut x2 = x[x_start - t];
    let mut x1 = x[x_start - t + 1];

    for (i, sample) in y.iter_mut().enumerate() {
        let x0 = x[x_start + i - t + 2];
        let mut acc = add32(x[x_start + i], mult16_32_q15(g10, x2));
        acc = add32(acc, mult16_32_q15(g11, add32(x1, x3)));
        acc = add32(acc, mult16_32_q15(g12, add32(x0, x4)));
        acc = sub32(acc, 1);
        *sample = saturate_sig(acc);

        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }
}

/// Fixed-point constant-coefficient comb filter operating in place.
///
/// Keeping the fixed-point decoder path on a single mutable channel buffer
/// matches the arithmetic structure of the C code while avoiding raw slice
/// reconstruction in Rust call sites.
#[cfg(feature = "fixed_point")]
pub(crate) fn comb_filter_const_fixed_in_place(
    channel: &mut [FixedCeltSig],
    output_start: usize,
    n: usize,
    t: usize,
    g10: FixedOpusVal16,
    g11: FixedOpusVal16,
    g12: FixedOpusVal16,
) {
    if n == 0 {
        return;
    }

    assert!(t >= COMBFILTER_MINPERIOD, "comb filter period too small");
    assert!(
        output_start >= t + 2,
        "channel does not provide enough history for the comb filter",
    );
    assert!(
        channel.len() >= output_start + n,
        "channel must provide output_start + n samples",
    );

    let mut x4 = channel[output_start - t - 2];
    let mut x3 = channel[output_start - t - 1];
    let mut x2 = channel[output_start - t];
    let mut x1 = channel[output_start - t + 1];

    for i in 0..n {
        let x0 = channel[output_start + i - t + 2];
        let mut acc = add32(channel[output_start + i], mult16_32_q15(g10, x2));
        acc = add32(acc, mult16_32_q15(g11, add32(x1, x3)));
        acc = add32(acc, mult16_32_q15(g12, add32(x0, x4)));
        acc = sub32(acc, 1);
        channel[output_start + i] = saturate_sig(acc);

        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }
}

/// Fixed-point variable tapset comb filter with optional overlap ramping.
///
/// Like [`comb_filter`], this variant is strictly out-of-place. Callers that
/// need same-buffer updates must use [`comb_filter_fixed_in_place`].
#[cfg(feature = "fixed_point")]
#[allow(clippy::too_many_arguments)]
pub(crate) fn comb_filter_fixed(
    y: &mut [FixedCeltSig],
    x: &[FixedCeltSig],
    x_start: usize,
    n: usize,
    mut t0: i32,
    mut t1: i32,
    g0: FixedOpusVal16,
    g1: FixedOpusVal16,
    tapset0: usize,
    tapset1: usize,
    window: &[FixedCeltCoef],
    overlap: usize,
    _arch: i32,
) {
    if n == 0 {
        return;
    }

    assert!(n <= y.len(), "output slice must hold n samples");
    assert!(x.len() >= x_start + n, "input slice must expose n samples");
    assert!(tapset0 < TAPSET_GAINS_FIXED.len(), "invalid tapset index");
    assert!(tapset1 < TAPSET_GAINS_FIXED.len(), "invalid tapset index");

    if g0 == 0 && g1 == 0 {
        let src = &x[x_start..x_start + n];
        let dst = &mut y[..n];
        debug_assert!(
            !slices_overlap(src, dst),
            "comb_filter_fixed requires distinct input/output slices; use comb_filter_fixed_in_place for overlap",
        );
        dst.copy_from_slice(src);
        return;
    }

    t0 = t0.max(COMBFILTER_MINPERIOD as i32);
    t1 = t1.max(COMBFILTER_MINPERIOD as i32);
    let t0 = t0 as usize;
    let t1 = t1 as usize;

    assert!(
        x_start >= t0 + 2 && x_start >= t1 + 2,
        "input slice lacks the required comb filter history",
    );

    let tap0 = TAPSET_GAINS_FIXED[tapset0];
    let tap1 = TAPSET_GAINS_FIXED[tapset1];
    let g00 = mult16_16_p15(g0, tap0[0]);
    let g01 = mult16_16_p15(g0, tap0[1]);
    let g02 = mult16_16_p15(g0, tap0[2]);
    let g10 = mult16_16_p15(g1, tap1[0]);
    let g11 = mult16_16_p15(g1, tap1[1]);
    let g12 = mult16_16_p15(g1, tap1[2]);

    let mut x1 = x[x_start - t1 + 1];
    let mut x2 = x[x_start - t1];
    let mut x3 = x[x_start - t1 - 1];
    let mut x4 = x[x_start - t1 - 2];

    let mut overlap = overlap.min(n);
    if g0 == g1 && t0 == t1 && tapset0 == tapset1 {
        overlap = 0;
    } else if overlap > 0 {
        assert!(
            window.len() >= overlap,
            "window must expose at least overlap samples",
        );
    }

    for i in 0..overlap {
        let x0 = x[x_start + i - t1 + 2];
        let f = mult16_16_q15(window[i], window[i]);
        let one_minus_f = (Q15_ONE as i32 - f as i32) as FixedOpusVal16;

        let current = x[x_start + i];
        let past0 = x[x_start + i - t0];
        let past1 = x[x_start + i - t0 + 1];
        let pastm1 = x[x_start + i - t0 - 1];
        let past2 = x[x_start + i - t0 + 2];
        let pastm2 = x[x_start + i - t0 - 2];

        let g00f = mult16_16_q15(one_minus_f, g00);
        let g01f = mult16_16_q15(one_minus_f, g01);
        let g02f = mult16_16_q15(one_minus_f, g02);
        let g10f = mult16_16_q15(f, g10);
        let g11f = mult16_16_q15(f, g11);
        let g12f = mult16_16_q15(f, g12);

        let mut acc = add32(current, mult16_32_q15(g00f, past0));
        acc = add32(acc, mult16_32_q15(g01f, add32(past1, pastm1)));
        acc = add32(acc, mult16_32_q15(g02f, add32(past2, pastm2)));
        acc = add32(acc, mult16_32_q15(g10f, x2));
        acc = add32(acc, mult16_32_q15(g11f, add32(x1, x3)));
        acc = add32(acc, mult16_32_q15(g12f, add32(x0, x4)));
        acc = sub32(acc, 3);
        y[i] = saturate_sig(acc);

        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }

    if g1 == 0 {
        if overlap < n {
            let src = &x[x_start + overlap..x_start + n];
            let dst = &mut y[overlap..n];
            debug_assert!(
                !slices_overlap(src, dst),
                "comb_filter_fixed requires distinct input/output slices; use comb_filter_fixed_in_place for overlap",
            );
            dst.copy_from_slice(src);
        }
        return;
    }

    if overlap < n {
        comb_filter_const_fixed(&mut y[overlap..n], x, x_start + overlap, t1, g10, g11, g12);
    }
}

/// Fixed-point variable tapset comb filter operating directly on one channel.
///
/// The decoder's fixed-point post-filter updates `decode_mem_fixed` in place.
/// This helper captures that ownership shape explicitly so the hot path stays
/// zero-copy and does not need aliasing `unsafe` at the call site.
#[cfg(feature = "fixed_point")]
#[allow(clippy::too_many_arguments)]
pub(crate) fn comb_filter_fixed_in_place(
    channel: &mut [FixedCeltSig],
    output_start: usize,
    n: usize,
    mut t0: i32,
    mut t1: i32,
    g0: FixedOpusVal16,
    g1: FixedOpusVal16,
    tapset0: usize,
    tapset1: usize,
    window: &[FixedCeltCoef],
    overlap: usize,
    _arch: i32,
) {
    if n == 0 {
        return;
    }

    assert!(
        channel.len() >= output_start + n,
        "channel must expose the requested output span",
    );
    assert!(tapset0 < TAPSET_GAINS_FIXED.len(), "invalid tapset index");
    assert!(tapset1 < TAPSET_GAINS_FIXED.len(), "invalid tapset index");

    if g0 == 0 && g1 == 0 {
        return;
    }

    t0 = t0.max(COMBFILTER_MINPERIOD as i32);
    t1 = t1.max(COMBFILTER_MINPERIOD as i32);
    let t0 = t0 as usize;
    let t1 = t1 as usize;

    assert!(
        output_start >= t0 + 2 && output_start >= t1 + 2,
        "channel lacks the required comb filter history",
    );

    let tap0 = TAPSET_GAINS_FIXED[tapset0];
    let tap1 = TAPSET_GAINS_FIXED[tapset1];
    let g00 = mult16_16_p15(g0, tap0[0]);
    let g01 = mult16_16_p15(g0, tap0[1]);
    let g02 = mult16_16_p15(g0, tap0[2]);
    let g10 = mult16_16_p15(g1, tap1[0]);
    let g11 = mult16_16_p15(g1, tap1[1]);
    let g12 = mult16_16_p15(g1, tap1[2]);

    let mut x1 = channel[output_start - t1 + 1];
    let mut x2 = channel[output_start - t1];
    let mut x3 = channel[output_start - t1 - 1];
    let mut x4 = channel[output_start - t1 - 2];

    let mut overlap = overlap.min(n);
    if g0 == g1 && t0 == t1 && tapset0 == tapset1 {
        overlap = 0;
    } else if overlap > 0 {
        assert!(
            window.len() >= overlap,
            "window must expose at least overlap samples",
        );
    }

    for i in 0..overlap {
        let x0 = channel[output_start + i - t1 + 2];
        let f = mult16_16_q15(window[i], window[i]);
        let one_minus_f = (Q15_ONE as i32 - f as i32) as FixedOpusVal16;

        let current = channel[output_start + i];
        let past0 = channel[output_start + i - t0];
        let past1 = channel[output_start + i - t0 + 1];
        let pastm1 = channel[output_start + i - t0 - 1];
        let past2 = channel[output_start + i - t0 + 2];
        let pastm2 = channel[output_start + i - t0 - 2];

        let g00f = mult16_16_q15(one_minus_f, g00);
        let g01f = mult16_16_q15(one_minus_f, g01);
        let g02f = mult16_16_q15(one_minus_f, g02);
        let g10f = mult16_16_q15(f, g10);
        let g11f = mult16_16_q15(f, g11);
        let g12f = mult16_16_q15(f, g12);

        let mut acc = add32(current, mult16_32_q15(g00f, past0));
        acc = add32(acc, mult16_32_q15(g01f, add32(past1, pastm1)));
        acc = add32(acc, mult16_32_q15(g02f, add32(past2, pastm2)));
        acc = add32(acc, mult16_32_q15(g10f, x2));
        acc = add32(acc, mult16_32_q15(g11f, add32(x1, x3)));
        acc = add32(acc, mult16_32_q15(g12f, add32(x0, x4)));
        acc = sub32(acc, 3);
        channel[output_start + i] = saturate_sig(acc);

        x4 = x3;
        x3 = x2;
        x2 = x1;
        x1 = x0;
    }

    if g1 == 0 {
        return;
    }

    if overlap < n {
        comb_filter_const_fixed_in_place(
            channel,
            output_start + overlap,
            n - overlap,
            t1,
            g10,
            g11,
            g12,
        );
    }
}

/// Fills `cap` with the per-band dynamic allocation caps for the provided mode.
///
/// Mirrors the behaviour of `init_caps()` from `celt/celt.c`, scaling the
/// cached limits by the number of channels and the effective band size derived
/// from `LM`. The caller must provide a `cap` slice whose length matches the
/// number of energy bands in the mode.
pub(crate) fn init_caps(mode: &OpusCustomMode<'_>, cap: &mut [i32], lm: usize, channels: usize) {
    let nb_ebands = mode.num_ebands;
    assert_eq!(cap.len(), nb_ebands, "cap slice must cover every band");
    assert!(channels > 0, "channel count must be positive");
    assert!(
        mode.e_bands.len() > nb_ebands,
        "mode does not expose the terminating band edge"
    );

    let stride = 2 * lm + (channels - 1);
    let base_offset = nb_ebands * stride;
    let caps_table = &mode.cache.caps;
    assert!(
        base_offset + nb_ebands <= caps_table.len(),
        "pulse cache caps table is too small"
    );

    for (band_index, cap_value) in cap.iter_mut().enumerate() {
        let band_width = i32::from(mode.e_bands[band_index + 1] - mode.e_bands[band_index]);
        let n = band_width << lm;
        let cached_cap = i32::from(caps_table[base_offset + band_index]) + 64;
        let scaled = cached_cap * (channels as i32) * n;
        *cap_value = scaled >> 2;
    }
}

/// Returns the downsampling factor that maps the 48 kHz reference rate to the
/// provided sampling rate.
///
/// Mirrors the behaviour of `resampling_factor()` from `celt/celt.c`, which is
/// used to derive the coarse pitch analysis stride. Unsupported sampling rates
/// fall back to zero just like the reference implementation when custom modes
/// are enabled.
#[must_use]
pub(crate) fn resampling_factor(rate: OpusInt32) -> u32 {
    match rate {
        48_000 => 1,
        24_000 => 2,
        16_000 => 3,
        12_000 => 4,
        8_000 => 6,
        _ => 0,
    }
}

#[cfg(test)]
mod tests {
    use super::{
        OPUS_VERSION_STRING, TF_SELECT_TABLE, comb_filter, comb_filter_const, comb_filter_in_place,
        init_caps, opus_get_version_string, opus_strerror, resampling_factor,
    };
    #[cfg(feature = "fixed_point")]
    use crate::celt::fixed_arch::{Q15_ONE, SIG_SAT};
    #[cfg(feature = "fixed_point")]
    use crate::celt::fixed_ops::{
        add32, mult16_16_p15, mult16_16_q15, mult16_32_q15, qconst16, sub32,
    };
    #[cfg(feature = "fixed_point")]
    use crate::celt::types::{FixedCeltCoef, FixedCeltSig, FixedOpusVal16};
    use crate::celt::types::{MdctLookup, OpusCustomMode, PulseCacheData};
    use alloc::vec::Vec;
    use alloc::{format, vec};

    const EPSILON: f32 = 1e-6;

    fn approx_eq(a: f32, b: f32) -> bool {
        (a - b).abs() <= EPSILON
    }

    fn comb_filter_const_reference(
        x: &[f32],
        x_start: usize,
        t: usize,
        n: usize,
        g10: f32,
        g11: f32,
        g12: f32,
    ) -> Vec<f32> {
        if n == 0 {
            return Vec::new();
        }

        let mut out = vec![0.0; n];
        let mut x4 = x[x_start - t - 2];
        let mut x3 = x[x_start - t - 1];
        let mut x2 = x[x_start - t];
        let mut x1 = x[x_start - t + 1];

        for i in 0..n {
            let current = x[x_start + i];
            let x0 = x[x_start + i - t + 2];
            out[i] = current + g10 * x2 + g11 * (x1 + x3) + g12 * (x0 + x4);
            x4 = x3;
            x3 = x2;
            x2 = x1;
            x1 = x0;
        }

        out
    }

    fn comb_filter_reference(
        x: &[f32],
        x_start: usize,
        n: usize,
        t0: i32,
        t1: i32,
        g0: f32,
        g1: f32,
        tapset0: usize,
        tapset1: usize,
        window: &[f32],
        overlap: usize,
    ) -> Vec<f32> {
        if n == 0 {
            return Vec::new();
        }

        if g0 == 0.0 && g1 == 0.0 {
            return x[x_start..x_start + n].to_vec();
        }

        let t0 = t0.max(super::COMBFILTER_MINPERIOD as i32) as usize;
        let t1 = t1.max(super::COMBFILTER_MINPERIOD as i32) as usize;

        let tap0 = super::TAPSET_GAINS[tapset0];
        let tap1 = super::TAPSET_GAINS[tapset1];
        let g00 = g0 * tap0[0];
        let g01 = g0 * tap0[1];
        let g02 = g0 * tap0[2];
        let g10 = g1 * tap1[0];
        let g11 = g1 * tap1[1];
        let g12 = g1 * tap1[2];

        let mut out = vec![0.0; n];

        let mut x1 = x[x_start - t1 + 1];
        let mut x2 = x[x_start - t1];
        let mut x3 = x[x_start - t1 - 1];
        let mut x4 = x[x_start - t1 - 2];

        let mut overlap = overlap.min(n);
        if g0 == g1 && t0 == t1 && tapset0 == tapset1 {
            overlap = 0;
        }

        for i in 0..overlap {
            let x0 = x[x_start + i - t1 + 2];
            let f = window[i] * window[i];
            let one_minus_f = 1.0 - f;

            let current = x[x_start + i];
            let past0 = x[x_start + i - t0];
            let past1 = x[x_start + i - t0 + 1];
            let pastm1 = x[x_start + i - t0 - 1];
            let past2 = x[x_start + i - t0 + 2];
            let pastm2 = x[x_start + i - t0 - 2];

            out[i] = current
                + one_minus_f * g00 * past0
                + one_minus_f * g01 * (past1 + pastm1)
                + one_minus_f * g02 * (past2 + pastm2)
                + f * g10 * x2
                + f * g11 * (x1 + x3)
                + f * g12 * (x0 + x4);

            x4 = x3;
            x3 = x2;
            x2 = x1;
            x1 = x0;
        }

        if g1 == 0.0 {
            if overlap < n {
                out[overlap..].copy_from_slice(&x[x_start + overlap..x_start + n]);
            }
            return out;
        }

        if overlap < n {
            let tail =
                comb_filter_const_reference(x, x_start + overlap, t1, n - overlap, g10, g11, g12);
            out[overlap..].copy_from_slice(&tail);
        }

        out
    }

    #[test]
    fn matches_reference_mapping() {
        assert_eq!(resampling_factor(48_000), 1);
        assert_eq!(resampling_factor(24_000), 2);
        assert_eq!(resampling_factor(16_000), 3);
        assert_eq!(resampling_factor(12_000), 4);
        assert_eq!(resampling_factor(8_000), 6);
    }

    #[test]
    fn returns_zero_for_unsupported_rates() {
        assert_eq!(resampling_factor(44_100), 0);
        assert_eq!(resampling_factor(96_000), 0);
    }

    #[test]
    fn tf_select_table_matches_reference_layout() {
        let expected = [
            [0, -1, 0, -1, 0, -1, 0, -1],
            [0, -1, 0, -2, 1, 0, 1, -1],
            [0, -2, 0, -3, 2, 0, 1, -1],
            [0, -2, 0, -3, 3, 0, 1, -1],
        ];
        assert_eq!(TF_SELECT_TABLE, expected);
    }

    #[test]
    fn init_caps_scales_cached_limits() {
        let e_bands = [0, 2, 5];
        let alloc_vectors = [0u8; 4];
        let log_n = [0i16; 2];
        let window = [0.0f32; 4];
        let mdct = MdctLookup::new(8, 0);
        let cache = PulseCacheData::new(vec![0; 6], vec![0; 6], vec![10, 20, 30, 40, 50, 60]);
        let mode = OpusCustomMode::new_test(
            48_000,
            4,
            &e_bands,
            &alloc_vectors,
            &log_n,
            &window,
            mdct,
            cache,
        );

        let mut caps = vec![0; mode.num_ebands];
        init_caps(&mode, &mut caps, 1, 1);

        assert_eq!(caps, [114, 186]);
    }

    #[test]
    fn opus_strerror_matches_reference_strings() {
        assert_eq!(opus_strerror(0), "success");
        assert_eq!(opus_strerror(-1), "invalid argument");
        assert_eq!(opus_strerror(-7), "memory allocation failed");
        assert_eq!(opus_strerror(1), "unknown error");
        assert_eq!(opus_strerror(-42), "unknown error");
    }

    #[test]
    fn opus_get_version_string_matches_constant() {
        assert_eq!(opus_get_version_string(), OPUS_VERSION_STRING);
        let expected = format!("libopus {}", env!("CARGO_PKG_VERSION"));
        assert_eq!(opus_get_version_string(), expected);
    }

    #[test]
    fn comb_filter_const_matches_reference() {
        let history = super::COMBFILTER_MINPERIOD + 2;
        let n = 6;
        let mut x = Vec::new();
        for i in 0..(history + n + 4) {
            x.push(i as f32 * 0.25);
        }

        let mut output = vec![0.0; n];
        let g10 = 0.45;
        let g11 = -0.2;
        let g12 = 0.05;

        comb_filter_const(
            &mut output,
            &x,
            history,
            super::COMBFILTER_MINPERIOD,
            g10,
            g11,
            g12,
        );

        let expected =
            comb_filter_const_reference(&x, history, super::COMBFILTER_MINPERIOD, n, g10, g11, g12);

        for (a, b) in output.iter().zip(expected.iter()) {
            assert!(approx_eq(*a, *b));
        }
    }

    #[test]
    fn comb_filter_matches_reference() {
        let t0 = 21;
        let t1 = 27;
        let history = (t1 as usize) + 3;
        let n = 12;
        let mut x = Vec::new();
        for i in 0..(history + n + 6) {
            x.push((i as f32 * 0.13).sin());
        }

        let mut y = vec![0.0; n];
        let g0 = 0.6;
        let g1 = 0.35;
        let tapset0 = 0;
        let tapset1 = 2;
        let window = [0.1, 0.4, 0.6, 0.7, 0.5, 0.2];
        let overlap = window.len();

        comb_filter(
            &mut y, &x, history, n, t0, t1, g0, g1, tapset0, tapset1, &window, overlap, 0,
        );

        let expected = comb_filter_reference(
            &x, history, n, t0, t1, g0, g1, tapset0, tapset1, &window, overlap,
        );

        for (a, b) in y.iter().zip(expected.iter()) {
            assert!(approx_eq(*a, *b));
        }
    }

    #[test]
    fn comb_filter_zero_gains_copy_input() {
        let history = super::COMBFILTER_MINPERIOD + 5;
        let n = 8;
        let mut x = Vec::new();
        for i in 0..(history + n) {
            x.push(i as f32 * 0.5);
        }

        let mut y = vec![0.0; n];
        comb_filter(&mut y, &x, history, n, 10, 12, 0.0, 0.0, 0, 1, &[], 0, 0);

        let expected = x[history..history + n].to_vec();
        assert_eq!(y, expected);
    }

    #[test]
    fn comb_filter_in_place_matches_reference() {
        let t0 = 21;
        let t1 = 27;
        let history = (t1 as usize) + 3;
        let n = 12;
        let mut channel = Vec::new();
        for i in 0..(history + n + 6) {
            channel.push((i as f32 * 0.13).sin());
        }

        let original = channel.clone();
        let g0 = 0.6;
        let g1 = 0.35;
        let tapset0 = 0;
        let tapset1 = 2;
        let window = [0.1, 0.4, 0.6, 0.7, 0.5, 0.2];
        let overlap = window.len();

        comb_filter_in_place(
            &mut channel,
            history,
            n,
            t0,
            t1,
            g0,
            g1,
            tapset0,
            tapset1,
            &window,
            overlap,
            0,
        );

        let expected = comb_filter_reference(
            &original, history, n, t0, t1, g0, g1, tapset0, tapset1, &window, overlap,
        );

        assert_eq!(&channel[..history], &original[..history]);
        for (actual, expected) in channel[history..history + n].iter().zip(expected.iter()) {
            assert!(approx_eq(*actual, *expected));
        }
    }

    #[test]
    fn comb_filter_in_place_zero_gains_noop() {
        let history = super::COMBFILTER_MINPERIOD + 5;
        let n = 8;
        let mut channel = Vec::new();
        for i in 0..(history + n) {
            channel.push(i as f32 * 0.5);
        }

        let original = channel.clone();
        comb_filter_in_place(&mut channel, history, n, 10, 12, 0.0, 0.0, 0, 1, &[], 0, 0);

        assert_eq!(channel, original);
    }

    #[cfg(feature = "fixed_point")]
    fn comb_filter_const_fixed_reference(
        y: &mut [FixedCeltSig],
        x: &[FixedCeltSig],
        x_start: usize,
        t: usize,
        g10: FixedOpusVal16,
        g11: FixedOpusVal16,
        g12: FixedOpusVal16,
    ) {
        let mut x4 = x[x_start - t - 2];
        let mut x3 = x[x_start - t - 1];
        let mut x2 = x[x_start - t];
        let mut x1 = x[x_start - t + 1];
        for i in 0..y.len() {
            let x0 = x[x_start + i - t + 2];
            let mut acc = add32(x[x_start + i], mult16_32_q15(g10, x2));
            acc = add32(acc, mult16_32_q15(g11, add32(x1, x3)));
            acc = add32(acc, mult16_32_q15(g12, add32(x0, x4)));
            acc = sub32(acc, 1);
            let acc = if acc > SIG_SAT {
                SIG_SAT
            } else if acc < -SIG_SAT {
                -SIG_SAT
            } else {
                acc
            };
            y[i] = acc;
            x4 = x3;
            x3 = x2;
            x2 = x1;
            x1 = x0;
        }
    }

    #[cfg(feature = "fixed_point")]
    fn comb_filter_fixed_reference(
        y: &mut [FixedCeltSig],
        x: &[FixedCeltSig],
        x_start: usize,
        n: usize,
        mut t0: i32,
        mut t1: i32,
        g0: FixedOpusVal16,
        g1: FixedOpusVal16,
        tapset0: usize,
        tapset1: usize,
        window: &[FixedCeltCoef],
        overlap: usize,
    ) {
        const TAPSET_GAINS_FIXED: [[FixedOpusVal16; 3]; 3] =
            [[10048, 7112, 4248], [15200, 8784, 0], [26208, 3280, 0]];

        if g0 == 0 && g1 == 0 {
            y[..n].copy_from_slice(&x[x_start..x_start + n]);
            return;
        }

        t0 = t0.max(super::COMBFILTER_MINPERIOD as i32);
        t1 = t1.max(super::COMBFILTER_MINPERIOD as i32);
        let t0 = t0 as usize;
        let t1 = t1 as usize;

        let tap0 = TAPSET_GAINS_FIXED[tapset0];
        let tap1 = TAPSET_GAINS_FIXED[tapset1];
        let g00 = mult16_16_p15(g0, tap0[0]);
        let g01 = mult16_16_p15(g0, tap0[1]);
        let g02 = mult16_16_p15(g0, tap0[2]);
        let g10 = mult16_16_p15(g1, tap1[0]);
        let g11 = mult16_16_p15(g1, tap1[1]);
        let g12 = mult16_16_p15(g1, tap1[2]);

        let mut x1 = x[x_start - t1 + 1];
        let mut x2 = x[x_start - t1];
        let mut x3 = x[x_start - t1 - 1];
        let mut x4 = x[x_start - t1 - 2];

        let mut overlap = overlap.min(n);
        if g0 == g1 && t0 == t1 && tapset0 == tapset1 {
            overlap = 0;
        }

        for i in 0..overlap {
            let x0 = x[x_start + i - t1 + 2];
            let f = mult16_16_q15(window[i], window[i]);
            let one_minus_f = (Q15_ONE as i32 - f as i32) as FixedOpusVal16;

            let current = x[x_start + i];
            let past0 = x[x_start + i - t0];
            let past1 = x[x_start + i - t0 + 1];
            let pastm1 = x[x_start + i - t0 - 1];
            let past2 = x[x_start + i - t0 + 2];
            let pastm2 = x[x_start + i - t0 - 2];

            let g00f = mult16_16_q15(one_minus_f, g00);
            let g01f = mult16_16_q15(one_minus_f, g01);
            let g02f = mult16_16_q15(one_minus_f, g02);
            let g10f = mult16_16_q15(f, g10);
            let g11f = mult16_16_q15(f, g11);
            let g12f = mult16_16_q15(f, g12);

            let mut acc = add32(current, mult16_32_q15(g00f, past0));
            acc = add32(acc, mult16_32_q15(g01f, add32(past1, pastm1)));
            acc = add32(acc, mult16_32_q15(g02f, add32(past2, pastm2)));
            acc = add32(acc, mult16_32_q15(g10f, x2));
            acc = add32(acc, mult16_32_q15(g11f, add32(x1, x3)));
            acc = add32(acc, mult16_32_q15(g12f, add32(x0, x4)));
            acc = sub32(acc, 3);
            let acc = if acc > SIG_SAT {
                SIG_SAT
            } else if acc < -SIG_SAT {
                -SIG_SAT
            } else {
                acc
            };
            y[i] = acc;

            x4 = x3;
            x3 = x2;
            x2 = x1;
            x1 = x0;
        }

        if g1 == 0 {
            if overlap < n {
                y[overlap..n].copy_from_slice(&x[x_start + overlap..x_start + n]);
            }
            return;
        }

        if overlap < n {
            comb_filter_const_fixed_reference(
                &mut y[overlap..n],
                x,
                x_start + overlap,
                t1,
                g10,
                g11,
                g12,
            );
        }
    }

    #[cfg(feature = "fixed_point")]
    #[test]
    fn comb_filter_fixed_matches_reference() {
        let history = 40usize;
        let n = 12usize;
        let mut x = vec![0i32; history + n + 8];
        for (i, slot) in x.iter_mut().enumerate() {
            let base = (i as i32 % 11) - 5;
            let bump = if i & 1 == 0 { -200 } else { 200 };
            *slot = base * 900 + bump;
        }
        let x_start = history;

        let g10 = qconst16(0.6, 15);
        let g11 = qconst16(-0.2, 15);
        let g12 = qconst16(0.1, 15);

        let mut y = vec![0i32; n];
        let mut expected = vec![0i32; n];
        super::comb_filter_const_fixed(&mut y, &x, x_start, 20, g10, g11, g12);
        comb_filter_const_fixed_reference(&mut expected, &x, x_start, 20, g10, g11, g12);
        assert_eq!(y, expected);

        let window: [FixedCeltCoef; 5] = [
            qconst16(0.05, 15),
            qconst16(0.25, 15),
            qconst16(0.5, 15),
            qconst16(0.75, 15),
            qconst16(0.9, 15),
        ];
        let g0 = qconst16(0.65, 15);
        let g1 = qconst16(-0.35, 15);
        super::comb_filter_fixed(
            &mut y,
            &x,
            x_start,
            n,
            18,
            26,
            g0,
            g1,
            0,
            2,
            &window,
            window.len(),
            0,
        );
        comb_filter_fixed_reference(
            &mut expected,
            &x,
            x_start,
            n,
            18,
            26,
            g0,
            g1,
            0,
            2,
            &window,
            window.len(),
        );
        assert_eq!(y, expected);

        let g0 = qconst16(0.45, 15);
        let g1 = 0i16;
        super::comb_filter_fixed(
            &mut y,
            &x,
            x_start,
            n,
            21,
            24,
            g0,
            g1,
            1,
            1,
            &window,
            window.len(),
            0,
        );
        comb_filter_fixed_reference(
            &mut expected,
            &x,
            x_start,
            n,
            21,
            24,
            g0,
            g1,
            1,
            1,
            &window,
            window.len(),
        );
        assert_eq!(y, expected);

        super::comb_filter_fixed(
            &mut y,
            &x,
            x_start,
            n,
            15,
            15,
            0,
            0,
            0,
            0,
            &window,
            window.len(),
            0,
        );
        expected.copy_from_slice(&x[x_start..x_start + n]);
        assert_eq!(y, expected);
    }

    #[cfg(feature = "fixed_point")]
    #[test]
    fn comb_filter_fixed_in_place_matches_reference() {
        let history = 40usize;
        let n = 12usize;
        let mut channel = vec![0i32; history + n + 8];
        for (i, slot) in channel.iter_mut().enumerate() {
            let base = (i as i32 % 11) - 5;
            let bump = if i & 1 == 0 { -200 } else { 200 };
            *slot = base * 900 + bump;
        }
        let original = channel.clone();
        let x_start = history;

        let window: [FixedCeltCoef; 5] = [
            qconst16(0.05, 15),
            qconst16(0.25, 15),
            qconst16(0.5, 15),
            qconst16(0.75, 15),
            qconst16(0.9, 15),
        ];
        let g0 = qconst16(0.65, 15);
        let g1 = qconst16(-0.35, 15);
        super::comb_filter_fixed_in_place(
            &mut channel,
            x_start,
            n,
            18,
            26,
            g0,
            g1,
            0,
            2,
            &window,
            window.len(),
            0,
        );

        let mut expected = vec![0i32; n];
        comb_filter_fixed_reference(
            &mut expected,
            &original,
            x_start,
            n,
            18,
            26,
            g0,
            g1,
            0,
            2,
            &window,
            window.len(),
        );

        assert_eq!(&channel[..x_start], &original[..x_start]);
        assert_eq!(&channel[x_start..x_start + n], expected.as_slice());
    }

    #[cfg(feature = "fixed_point")]
    #[test]
    fn comb_filter_fixed_in_place_zero_gains_noop() {
        let history = 40usize;
        let n = 12usize;
        let mut channel = vec![0i32; history + n + 8];
        for (i, slot) in channel.iter_mut().enumerate() {
            *slot = (i as i32 - 11) * 73;
        }

        let original = channel.clone();
        let window: [FixedCeltCoef; 5] = [
            qconst16(0.05, 15),
            qconst16(0.25, 15),
            qconst16(0.5, 15),
            qconst16(0.75, 15),
            qconst16(0.9, 15),
        ];
        super::comb_filter_fixed_in_place(
            &mut channel,
            history,
            n,
            15,
            15,
            0,
            0,
            0,
            0,
            &window,
            window.len(),
            0,
        );

        assert_eq!(channel, original);
    }
}