zrip-core 0.4.0

Shared types and codecs for zrip (internal crate)
Documentation 
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#![forbid(unsafe_code)]

#[cfg(feature = "alloc")]
use alloc::vec::Vec;

use super::primitives;

pub struct BitWriter {
    #[cfg(feature = "alloc")]
    buf: Vec<u8>,
    bits: u64,
    bits_used: u8,
    pos: usize,
}

#[cfg(feature = "alloc")]
impl Default for BitWriter {
    fn default() -> Self {
        Self::new()
    }
}

#[cfg(feature = "alloc")]
impl BitWriter {
    pub fn new() -> Self {
        Self {
            buf: Vec::with_capacity(64),
            bits: 0,
            bits_used: 0,
            pos: 0,
        }
    }

    pub fn with_capacity(cap: usize) -> Self {
        Self {
            buf: Vec::with_capacity(cap + 8),
            bits: 0,
            bits_used: 0,
            pos: 0,
        }
    }

    pub fn from_vec(mut buf: Vec<u8>) -> Self {
        buf.clear();
        buf.reserve(8);
        Self {
            buf,
            bits: 0,
            bits_used: 0,
            pos: 0,
        }
    }

    pub fn into_vec(mut self) -> Vec<u8> {
        self.flush_remaining();
        self.buf
    }

    #[inline(always)]
    fn ensure_capacity(&mut self) {
        if self.pos + 8 > self.buf.capacity() {
            primitives::set_vec_len(&mut self.buf, self.pos);
            self.buf.reserve(64);
        }
    }

    #[inline(always)]
    pub fn write_bits(&mut self, value: u32, n: u8) {
        debug_assert!(n <= 25);
        if n == 0 {
            return;
        }
        debug_assert!(value < (1u32 << n));
        self.bits |= (value as u64) << self.bits_used;
        self.bits_used += n;
        if self.bits_used >= 32 {
            self.ensure_capacity();
            primitives::write_u64_le_unaligned(&mut self.buf, self.pos, self.bits);
            let nb = (self.bits_used >> 3) as usize;
            self.pos += nb;
            self.bits >>= nb << 3;
            self.bits_used &= 7;
        }
    }

    pub fn flush_remaining(&mut self) {
        primitives::set_vec_len(&mut self.buf, self.pos);
        while self.bits_used > 0 {
            self.buf.push(self.bits as u8);
            self.bits >>= 8;
            self.bits_used = self.bits_used.saturating_sub(8);
        }
        self.pos = self.buf.len();
    }

    pub fn close_reverse_stream(&mut self) {
        self.write_bits(1, 1);
        self.flush_remaining();
    }

    pub fn bits_written(&self) -> usize {
        self.pos * 8 + self.bits_used as usize
    }

    pub fn into_bytes(mut self) -> Vec<u8> {
        self.flush_remaining();
        self.buf
    }

    pub fn as_bytes(&mut self) -> &[u8] {
        primitives::set_vec_len(&mut self.buf, self.pos);
        &self.buf
    }

    pub fn write_byte(&mut self, b: u8) {
        self.write_bits(b as u32, 8);
    }

    pub fn write_bytes(&mut self, bytes: &[u8]) {
        for &b in bytes {
            self.write_byte(b);
        }
    }
}

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

    #[test]
    fn write_and_read_back() {
        let mut w = BitWriter::new();
        w.write_bits(0b101, 3);
        w.write_bits(0b11, 2);
        w.write_bits(0b000, 3);
        let bytes = w.into_bytes();
        assert_eq!(bytes, [0b0001_1101]);
    }

    #[test]
    fn write_cross_byte() {
        let mut w = BitWriter::new();
        w.write_bits(0xFF, 8);
        w.write_bits(0x01, 8);
        let bytes = w.into_bytes();
        assert_eq!(bytes, [0xFF, 0x01]);
    }

    #[test]
    fn write_partial() {
        let mut w = BitWriter::new();
        w.write_bits(0b1, 1);
        let bytes = w.into_bytes();
        assert_eq!(bytes, [0b0000_0001]);
    }

    #[test]
    fn reverse_stream_roundtrip() {
        use crate::bitstream::reader_reverse::ReverseBitReader;

        let mut w = BitWriter::new();
        w.write_bits(0b1010, 4);
        w.write_bits(0b0101, 4);
        w.close_reverse_stream();
        let bytes = w.into_bytes();

        let mut r = ReverseBitReader::new(&bytes).unwrap();
        assert_eq!(r.read_bits(4).unwrap(), 0b0101);
        assert_eq!(r.read_bits(4).unwrap(), 0b1010);
        assert_eq!(r.bits_remaining(), 0);
    }
}