94 lines
3.9 KiB
Markdown
94 lines
3.9 KiB
Markdown
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# crc32fast [![Build Status][travis-img]][travis] [![Crates.io][crates-img]][crates] [![Documentation][docs-img]][docs]
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[travis-img]: https://travis-ci.com/srijs/rust-crc32fast.svg?branch=master
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[travis]: https://travis-ci.com/srijs/rust-crc32fast
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[crates-img]: https://img.shields.io/crates/v/crc32fast.svg
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[crates]: https://crates.io/crates/crc32fast
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[docs-img]: https://docs.rs/crc32fast/badge.svg
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[docs]: https://docs.rs/crc32fast
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_Fast, SIMD-accelerated CRC32 (IEEE) checksum computation_
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## Usage
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### Simple usage
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For simple use-cases, you can call the `hash` convenience function to
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directly compute the CRC32 checksum for a given byte slice:
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```rust
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let checksum = crc32fast::hash(b"foo bar baz");
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```
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### Advanced usage
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For use-cases that require more flexibility or performance, for example when
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processing large amounts of data, you can create and manipulate a `Hasher`:
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```rust
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use crc32fast::Hasher;
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let mut hasher = Hasher::new();
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hasher.update(b"foo bar baz");
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let checksum = hasher.finalize();
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```
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## Performance
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This crate contains multiple CRC32 implementations:
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- A fast baseline implementation which processes up to 16 bytes per iteration
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- An optimized implementation for modern `x86` using `sse` and `pclmulqdq` instructions
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- An optimized implementation for `aarch64` using `crc32` instructions
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Calling the `Hasher::new` constructor at runtime will perform a feature detection to select the most
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optimal implementation for the current CPU feature set.
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| crate | version | variant | ns/iter | MB/s |
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| ----------------------------------- | ------- | --------- | ------- | ---- |
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| [crc](https://crates.io/crates/crc) | 1.8.1 | n/a | 4,926 | 207 |
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| crc32fast (this crate) | 1.0.0 | baseline | 683 | 1499 |
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| crc32fast (this crate) | 1.0.0 | pclmulqdq | 140 | 7314 |
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## Memory Safety
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Due to the use of SIMD intrinsics for the optimized implementations, this crate contains some amount of `unsafe` code.
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In order to ensure memory safety, the relevant code has been fuzz tested using [afl.rs](https://github.com/rust-fuzz/afl.rs) with millions of iterations in both `debug` and `release` build settings. You can inspect the test setup in the `fuzz` sub-directory, which also has instructions on how to run the tests yourself.
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On top of that, every commit is tested using an address sanitizer in CI to catch any out of bounds memory accesses.
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Even though neither fuzzing nor sanitization has revealed any safety bugs yet, please don't hesitate to file an issue if you run into any crashes or other unexpected behaviour.
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## Available feature flags
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### `std` (default: enabled)
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This library supports being built without the Rust `std` library, which is useful for low-level use-cases such as embedded where no operating system is available. To build the crate in a `no_std` context, disable the default `std` feature.
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Note: Because runtime CPU feature detection requires OS support, the specialized SIMD implementations will be unavailable when the `std` feature is disabled.
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### `nightly` (default: disabled)
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This feature flag enables unstable features that are only available on the `nightly` channel. Keep in mind that when enabling this feature flag, you
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might experience breaking changes when updating compiler versions.
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Currently, enabling this feature flag will make the optimized `aarch64` implementation available.
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## License
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This project is licensed under either of
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- Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
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http://www.apache.org/licenses/LICENSE-2.0)
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- MIT license ([LICENSE-MIT](LICENSE-MIT) or
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http://opensource.org/licenses/MIT)
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at your option.
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### Contribution
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in this project by you, as defined in the Apache-2.0 license,
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shall be dual licensed as above, without any additional terms or conditions.
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