zrip_core/fse/
decode.rs

1#![forbid(unsafe_code)]
2
3use crate::bitstream::reader_reverse::ReverseBitReader;
4use crate::error::DecompressError;
5use crate::fse::FseDecodeEntry;
6
7pub struct FseState<'t> {
8    table: &'t [FseDecodeEntry],
9    state: u32,
10}
11
12impl<'t> FseState<'t> {
13    pub fn new(
14        table: &'t [FseDecodeEntry],
15        accuracy_log: u8,
16        reader: &mut ReverseBitReader,
17    ) -> Result<Self, DecompressError> {
18        let state = reader.read_bits(accuracy_log)?;
19        Ok(Self { table, state })
20    }
21
22    #[inline]
23    pub fn symbol(&self) -> u8 {
24        self.table[self.state as usize].symbol
25    }
26
27    #[inline]
28    pub fn num_bits(&self) -> u8 {
29        self.table[self.state as usize].num_bits
30    }
31
32    #[inline]
33    pub fn update_state(&mut self, reader: &mut ReverseBitReader) -> Result<(), DecompressError> {
34        let entry = &self.table[self.state as usize];
35        let bits = reader.read_bits(entry.num_bits)?;
36        self.state = entry.base_line as u32 + bits;
37        Ok(())
38    }
39
40    pub fn state(&self) -> u32 {
41        self.state
42    }
43}
44
45#[cfg(test)]
46mod tests {
47    use super::*;
48    use crate::bitstream::writer::BitWriter;
49    use crate::fse::table_builder::build_decode_table_from_default;
50    use crate::fse::{LL_DEFAULT_ACCURACY, LL_DEFAULT_DIST};
51
52    #[test]
53    fn init_and_read_symbol() {
54        let table = build_decode_table_from_default(&LL_DEFAULT_DIST, LL_DEFAULT_ACCURACY);
55
56        let mut w = BitWriter::new();
57        w.write_bits(0, LL_DEFAULT_ACCURACY);
58        w.close_reverse_stream();
59        let data = w.into_bytes();
60
61        let mut reader = ReverseBitReader::new(&data).unwrap();
62        let state = FseState::new(&table, LL_DEFAULT_ACCURACY, &mut reader).unwrap();
63        let sym = state.symbol();
64        assert!(sym <= 35);
65    }
66}
zrip_core/fse/decode.rs

zrip_core/fse/
decode.rs
