81 lines
3.3 KiB
Markdown
81 lines
3.3 KiB
Markdown
hashbrown
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=========
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[](https://github.com/rust-lang/hashbrown/actions)
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[](https://crates.io/crates/hashbrown)
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[](https://docs.rs/hashbrown)
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[](https://github.com/rust-lang/hashbrown)
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This crate is a Rust port of Google's high-performance [SwissTable] hash
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map, adapted to make it a drop-in replacement for Rust's standard `HashMap`
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and `HashSet` types.
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The original C++ version of SwissTable can be found [here], and this
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[CppCon talk] gives an overview of how the algorithm works.
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Since Rust 1.36, this is now the `HashMap` implementation for the Rust standard
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library. However you may still want to use this crate instead since it works
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in environments without `std`, such as embedded systems and kernels.
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[SwissTable]: https://abseil.io/blog/20180927-swisstables
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[here]: https://github.com/abseil/abseil-cpp/blob/master/absl/container/internal/raw_hash_set.h
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[CppCon talk]: https://www.youtube.com/watch?v=ncHmEUmJZf4
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## [Change log](CHANGELOG.md)
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## Features
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- Drop-in replacement for the standard library `HashMap` and `HashSet` types.
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- Uses [foldhash](https://github.com/orlp/foldhash) as the default hasher, which is much faster than SipHash.
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However, foldhash does *not provide the same level of HashDoS resistance* as SipHash, so if that is important to you, you might want to consider using a different hasher.
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- Around 2x faster than the previous standard library `HashMap`.
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- Lower memory usage: only 1 byte of overhead per entry instead of 8.
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- Compatible with `#[no_std]` (but requires a global allocator with the `alloc` crate).
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- Empty hash maps do not allocate any memory.
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- SIMD lookups to scan multiple hash entries in parallel.
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## Usage
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Add this to your `Cargo.toml`:
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```toml
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[dependencies]
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hashbrown = "0.15"
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```
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Then:
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```rust
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use hashbrown::HashMap;
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let mut map = HashMap::new();
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map.insert(1, "one");
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```
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## Flags
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This crate has the following Cargo features:
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- `nightly`: Enables nightly-only features including: `#[may_dangle]`.
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- `serde`: Enables serde serialization support.
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- `rayon`: Enables rayon parallel iterator support.
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- `equivalent`: Allows comparisons to be customized with the `Equivalent` trait. (enabled by default)
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- `raw-entry`: Enables access to the deprecated `RawEntry` API.
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- `inline-more`: Adds inline hints to most functions, improving run-time performance at the cost
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of compilation time. (enabled by default)
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- `default-hasher`: Compiles with foldhash as default hasher. (enabled by default)
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- `allocator-api2`: Enables support for allocators that support `allocator-api2`. (enabled by default)
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## License
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Licensed under either of:
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* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or https://www.apache.org/licenses/LICENSE-2.0)
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* MIT license ([LICENSE-MIT](LICENSE-MIT) or https://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 the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any
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additional terms or conditions.
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