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#![warn(missing_docs)]
pub use self::default::{DefaultLz77Encoder, DefaultLz77EncoderBuilder};
use rle_decode_fast::rle_decode;
mod default;
pub const MAX_LENGTH: u16 = 258;
pub const MAX_DISTANCE: u16 = 32_768;
pub const MAX_WINDOW_SIZE: u16 = MAX_DISTANCE;
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
pub enum Code {
Literal(u8),
Pointer {
length: u16,
backward_distance: u16,
},
}
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub enum CompressionLevel {
None,
Fast,
Balance,
Best,
}
pub trait Sink {
fn consume(&mut self, code: Code);
}
impl<'a, T> Sink for &'a mut T
where
T: Sink,
{
fn consume(&mut self, code: Code) {
(*self).consume(code);
}
}
impl<T> Sink for Vec<T>
where
T: From<Code>,
{
fn consume(&mut self, code: Code) {
self.push(T::from(code));
}
}
pub trait Lz77Encode {
fn encode<S>(&mut self, buf: &[u8], sink: S)
where
S: Sink;
fn flush<S>(&mut self, sink: S)
where
S: Sink;
fn compression_level(&self) -> CompressionLevel {
CompressionLevel::Balance
}
fn window_size(&self) -> u16 {
MAX_WINDOW_SIZE
}
}
#[derive(Debug, Default)]
pub struct NoCompressionLz77Encoder;
impl NoCompressionLz77Encoder {
pub fn new() -> Self {
NoCompressionLz77Encoder
}
}
impl Lz77Encode for NoCompressionLz77Encoder {
fn encode<S>(&mut self, buf: &[u8], mut sink: S)
where
S: Sink,
{
for c in buf.iter().cloned().map(Code::Literal) {
sink.consume(c);
}
}
#[allow(unused_variables)]
fn flush<S>(&mut self, sink: S)
where
S: Sink,
{
}
fn compression_level(&self) -> CompressionLevel {
CompressionLevel::None
}
}
#[derive(Debug, Default)]
pub struct Lz77Decoder {
buffer: Vec<u8>,
offset: usize,
}
impl Lz77Decoder {
pub fn new() -> Self {
Self::default()
}
#[inline]
pub fn decode(&mut self, code: Code) -> std::io::Result<()> {
match code {
Code::Literal(b) => {
self.buffer.push(b);
}
Code::Pointer {
length,
backward_distance,
} => {
if self.buffer.len() < backward_distance as usize {
return Err(std::io::Error::new(
std::io::ErrorKind::InvalidData,
format!(
"Too long backword reference: buffer.len={}, distance={}",
self.buffer.len(),
backward_distance
),
));
}
rle_decode(
&mut self.buffer,
usize::from(backward_distance),
usize::from(length),
);
}
}
Ok(())
}
pub fn extend_from_reader<R: std::io::Read>(
&mut self,
mut reader: R,
) -> std::io::Result<usize> {
reader.read_to_end(&mut self.buffer)
}
pub fn extend_from_slice(&mut self, buf: &[u8]) {
self.buffer.extend_from_slice(buf);
self.offset += buf.len();
}
pub fn clear(&mut self) {
self.buffer.clear();
self.offset = 0;
}
#[inline]
pub fn buffer(&self) -> &[u8] {
&self.buffer[self.offset..]
}
fn truncate_old_buffer(&mut self) {
if self.buffer().is_empty() && self.buffer.len() > MAX_DISTANCE as usize * 4 {
let old_len = self.buffer.len();
let new_len = MAX_DISTANCE as usize;
{
let (dst, src) = self.buffer.split_at_mut(old_len - new_len);
dst[..new_len].copy_from_slice(src);
}
self.buffer.truncate(new_len);
self.offset = new_len;
}
}
}
impl std::io::Read for Lz77Decoder {
fn read(&mut self, buf: &mut [u8]) -> std::io::Result<usize> {
let copy_size = std::cmp::min(buf.len(), self.buffer.len() - self.offset);
buf[..copy_size].copy_from_slice(&self.buffer[self.offset..][..copy_size]);
self.offset += copy_size;
self.truncate_old_buffer();
Ok(copy_size)
}
}
#[cfg(test)]
mod tests {
use super::*;
use std::io::Read as _;
#[test]
fn encoder_and_decoder_works() {
let mut codes = Vec::new();
let mut encoder = DefaultLz77Encoder::new();
encoder.encode(b"hello world!", &mut codes);
encoder.flush(&mut codes);
assert!(!codes.is_empty());
let mut decoder = Lz77Decoder::new();
for code in codes {
decoder.decode(code).unwrap();
}
assert_eq!(decoder.buffer(), b"hello world!");
let mut decoded = Vec::new();
decoder.read_to_end(&mut decoded).unwrap();
assert_eq!(decoded, b"hello world!");
assert!(decoder.buffer().is_empty());
}
}