interleaver.rs

use arrayvec::ArrayVec;
use bitvec::prelude::*;

use crate::error::EncodeError;

pub(crate) fn interleave<const N: usize>(
    data: &[u8],
    out: &mut ArrayVec<u8, N>,
) -> Result<(), EncodeError> {
    let bv = data.view_bits::<Msb0>();

    let initial_length = out.len();
    for _ in 0..data.len() {
        out.try_push(0).map_err(|_| EncodeError::CatsOverflow)?;
    }
    let bv_out = out[initial_length..].view_bits_mut::<Msb0>();

    let mut out_i = 0;
    for i in 0..32 {
        for j in (0..bv.len()).step_by(32) {
            if i + j >= bv.len() {
                continue;
            }

            bv_out.set(out_i, bv[i + j]);

            out_i += 1;
        }
    }

    Ok(())
}

pub(crate) fn uninterleave<const N: usize>(data: &[u8]) -> ArrayVec<u8, N> {
    let bv = data.view_bits::<Msb0>();

    let mut out: ArrayVec<u8, N> = ArrayVec::new();
    for _ in 0..data.len() {
        out.push(0);
    }
    let bv_out = out.view_bits_mut::<Msb0>();

    let mut out_i = 0;
    for i in 0..32 {
        for j in (0..bv.len()).step_by(32) {
            if i + j >= bv.len() {
                continue;
            }

            bv_out.set(i + j, bv[out_i]);

            out_i += 1;
        }
    }

    out
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn interleaver_works() {
        let orig =
            ArrayVec::try_from([0x84, 0x73, 0x12, 0xA3, 0xFF, 0x00, 0xC2, 0x1B, 0x77]).unwrap();
        let mut interleaved: ArrayVec<u8, 10> = ArrayVec::new();
        interleaved.push(b'H');
        interleave(&orig, &mut interleaved).unwrap();

        let expected = [b'H', 0xCD, 0xB5, 0xDB, 0x2A, 0x0A, 0x52, 0x0C, 0x89, 0x4F];
        assert_eq!(expected, interleaved[..]);

        let uninterleaved = uninterleave(&interleaved[1..]);

        assert_eq!(orig, uninterleaved);
    }
}