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comparison src/util/lzss.rs @ 637:afa012bb8021

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Hello Rust!
author Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
date Wed, 03 Jul 2019 16:27:12 +0200
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636:4fa0a8e7d941 637:afa012bb8021
1 //! LZSS implementation.
2
3 use std::io;
4 use crate::util::bitstream::BitStream;
5
6 /// Decompresses a LZSS-compressed file.
7 pub fn decompress<R: io::Read + io::Seek>(bitstream: &mut BitStream<R>, size: usize, dictionary_size: usize, offset_size: usize, length_size: usize, minimum_match_length: usize) -> io::Result<Vec<u8>> {
8 let mut data = vec![0; size];
9 let mut dictionary = vec![0; dictionary_size];
10 let mut dictionary_head = 1;
11 let mut ptr = 0;
12
13 while ptr < size {
14 if bitstream.read_bit()? {
15 // The `flag` bit is set, indicating the upcoming chunk of data is a literal.
16 // Add it to the uncompressed file, and store it in the dictionary.
17 let byte = bitstream.read(8)? as u8;
18 dictionary[dictionary_head] = byte;
19 dictionary_head = (dictionary_head + 1) % dictionary_size;
20 data[ptr] = byte;
21 ptr += 1;
22 } else {
23 // The `flag` bit is not set, the upcoming chunk is a (offset, length) tuple.
24 let offset = bitstream.read(offset_size)?;
25 let length = bitstream.read(length_size)? + minimum_match_length;
26 if ptr + length > size {
27 return Err(io::Error::new(io::ErrorKind::Other, "Oh no!"));
28 }
29 if offset == 0 && length == 0 {
30 break;
31 }
32 for i in offset..offset + length {
33 data[ptr] = dictionary[i % dictionary_size];
34 dictionary[dictionary_head] = dictionary[i % dictionary_size];
35 dictionary_head = (dictionary_head + 1) % dictionary_size;
36 ptr += 1;
37 }
38 }
39 }
40
41 Ok(data)
42 }
43
44 #[cfg(test)]
45 mod tests {
46 use super::*;
47 use crate::util::SeekableSlice;
48
49 #[test]
50 #[ignore]
51 fn bit_by_bit() {
52 // TODO: find actual lzss data.
53 let data = SeekableSlice::new(&[0, 0, 0]);
54 let mut bitstream = BitStream::new(data);
55 decompress(&mut bitstream, 3, 0x2000, 13, 4, 3).unwrap();
56 }
57 }