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annotate src/util/lzss.rs @ 725:fbf89cba04e2

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ecl_vm: some work on spellcard 11
author Gauvain "GovanifY" Roussel-Tarbouriech <gauvain@govanify.com>
date Tue, 29 Oct 2019 15:41:23 +0100
parents afa012bb8021
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
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1 //! LZSS implementation.
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2
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3 use std::io;
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4 use crate::util::bitstream::BitStream;
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5
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6 /// Decompresses a LZSS-compressed file.
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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>> {
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8 let mut data = vec![0; size];
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9 let mut dictionary = vec![0; dictionary_size];
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10 let mut dictionary_head = 1;
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11 let mut ptr = 0;
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12
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13 while ptr < size {
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14 if bitstream.read_bit()? {
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15 // The `flag` bit is set, indicating the upcoming chunk of data is a literal.
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16 // Add it to the uncompressed file, and store it in the dictionary.
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17 let byte = bitstream.read(8)? as u8;
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18 dictionary[dictionary_head] = byte;
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19 dictionary_head = (dictionary_head + 1) % dictionary_size;
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20 data[ptr] = byte;
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21 ptr += 1;
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22 } else {
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23 // The `flag` bit is not set, the upcoming chunk is a (offset, length) tuple.
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24 let offset = bitstream.read(offset_size)?;
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25 let length = bitstream.read(length_size)? + minimum_match_length;
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26 if ptr + length > size {
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27 return Err(io::Error::new(io::ErrorKind::Other, "Oh no!"));
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28 }
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29 if offset == 0 && length == 0 {
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30 break;
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31 }
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32 for i in offset..offset + length {
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33 data[ptr] = dictionary[i % dictionary_size];
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34 dictionary[dictionary_head] = dictionary[i % dictionary_size];
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35 dictionary_head = (dictionary_head + 1) % dictionary_size;
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36 ptr += 1;
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37 }
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38 }
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39 }
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40
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41 Ok(data)
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42 }
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43
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44 #[cfg(test)]
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45 mod tests {
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46 use super::*;
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47 use crate::util::SeekableSlice;
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48
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49 #[test]
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50 #[ignore]
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51 fn bit_by_bit() {
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52 // TODO: find actual lzss data.
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53 let data = SeekableSlice::new(&[0, 0, 0]);
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54 let mut bitstream = BitStream::new(data);
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55 decompress(&mut bitstream, 3, 0x2000, 13, 4, 3).unwrap();
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56 }
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57 }