https://github.com/wanzenbug/rle-decode-helper

THE fastest way to implement any kind of decoding for Run Length Encoded data in Rust.
https://github.com/wanzenbug/rle-decode-helper

inflate runlengthencoding rust

Last synced: 9 days ago
JSON representation

THE fastest way to implement any kind of decoding for Run Length Encoded data in Rust.

• Host: GitHub
• URL: https://github.com/wanzenbug/rle-decode-helper
• Owner: WanzenBug
• License: other
• Created: 2019-06-26T15:25:03.000Z (over 5 years ago)
• Default Branch: master
• Last Pushed: 2022-01-30T22:57:03.000Z (almost 3 years ago)
• Last Synced: 2024-10-08T10:23:47.498Z (about 1 month ago)
• Topics: inflate, runlengthencoding, rust
• Language: Rust
• Homepage:
• Size: 131 KB
• Stars: 6
• Watchers: 1
• Forks: 2
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • License: LICENSE-APACHE

Awesome Lists containing this project

README

        
# rle-decode-fast

**The same functionallity [is available in stable Rust](https://doc.rust-lang.org/alloc/vec/struct.Vec.html#method.extend_from_within) since 1.53, use that instead**

**THE** fastest way to implement any kind of decoding for **R**un **L**ength **E**ncoded data in Rust.

Writing a fast decoder that is also safe can be quite challenging, so this crate is here to save you the

hassle of maintaining and testing your own implementation.

## Usage

Of course, you need to depend on this crate:

```toml

rle-decode-fast = "1.0"

```

There is only a single function to use, `rle_decode(&mut Vec, lookbehind_size: usize, fill_length: usize)`. 

It takes :

* a vector to modify, 

* the number of items to copy from said vector (basically `vector[(vector.len() - lookbehind)..])`

* the number of items to append.

Afterwards the vector will contain an extra `fill_length` items.

```rust

use rle_decode_fast::rle_decode;

let mut decode_buffer = vec![0, 0, 1, 1, 0, 2, 3];

let lookbehind_length = 4;

let output_length = 10;

rle_decode(&mut decode_buffer, lookbehind_length, output_length);

assert_eq!(decode_buffer, [0, 0, 1, 1, 0, 2, 3, 1, 0, 2, 3, 1, 0, 2, 3, 1, 0]);

```

### Panics

There are cases where the decode functions panics

* The lookbehind length is 0

* The lookbehind length is bigger than the Vec's length

* The output length + Vec's length would overflow

## Background

The idea for this crate first originated from [this pre-RFC](https://internals.rust-lang.org/t/pre-rfc-fixed-capacity-view-of-vec/8413).

It brought to attention a weak-point in the standard library, which lead some crates writing their own unsafe by-pass.

During the exploration happening in the pre-RFC, some experimentation was conducted. For examples see [here](https://github.com/WanzenBug/rust-fixed-capacity-vec) and [here](https://docs.rs/buffer/0.1.8/buffer/).

## Some Stats

There is a benchmark comparing a naive (repeated push) implementation, a vulnerable implementation that might lead to

uninitialized memory and this crate.

The results for a very small fill length

![lookbehind=333](docs/benchmark-big-lb-small-length.PNG)

and for a bigger fill lengths

![lookbehind=2](docs/benchmark-big-lb-big-length.PNG)

## License

Licensed under either of

 * Apache License, Version 2.0

   [LICENSE-APACHE](LICENSE-APACHE)

 * MIT license

   [LICENSE-MIT](LICENSE-MIT)

at your option.

## Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted

for inclusion in the work by you, as defined in the Apache-2.0 license, shall be

dual licensed as above, without any additional terms or conditions.