92 lines
3.4 KiB
Markdown
92 lines
3.4 KiB
Markdown
# hashbrown
|
|
|
|
[](https://github.com/rust-lang/hashbrown/actions)
|
|
[](https://crates.io/crates/hashbrown)
|
|
[](https://docs.rs/hashbrown)
|
|
[](https://github.com/rust-lang/hashbrown)
|
|
|
|
This crate is a Rust port of Google's high-performance [SwissTable] hash map,
|
|
adapted to make it a drop-in replacement for Rust's standard `HashMap` and
|
|
`HashSet` types.
|
|
|
|
The original C++ version of SwissTable can be found [here], and this
|
|
[CppCon talk] gives an overview of how the algorithm works.
|
|
|
|
Since Rust 1.36, the Rust standard library has adopted this implementation for
|
|
`HashMap`, using its own default hasher (see
|
|
[`std::hash::DefaultHasher`](https://doc.rust-lang.org/std/hash/struct.DefaultHasher.html)).
|
|
However you may still want to use this crate instead since it works in
|
|
environments without `std`, such as embedded systems and kernels.
|
|
|
|
[SwissTable]: https://abseil.io/blog/20180927-swisstables
|
|
[here]: https://github.com/abseil/abseil-cpp/blob/master/absl/container/internal/raw_hash_set.h
|
|
[CppCon talk]: https://www.youtube.com/watch?v=ncHmEUmJZf4
|
|
|
|
## [Change log](CHANGELOG.md)
|
|
|
|
## Features
|
|
|
|
- Drop-in replacement for the standard library `HashMap` and `HashSet` types.
|
|
- Uses [foldhash](https://github.com/orlp/foldhash) as the default hasher, which
|
|
is much faster than SipHash. 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.
|
|
- Around 2x faster than the previous standard library `HashMap`.
|
|
- Lower memory usage: only 1 byte of overhead per entry instead of 8.
|
|
- Compatible with `#[no_std]` (but requires a global allocator with the `alloc`
|
|
crate).
|
|
- Empty hash maps do not allocate any memory.
|
|
- SIMD lookups to scan multiple hash entries in parallel.
|
|
|
|
## Usage
|
|
|
|
Add this to your `Cargo.toml`:
|
|
|
|
```toml
|
|
[dependencies]
|
|
hashbrown = "0.17"
|
|
```
|
|
|
|
Then:
|
|
|
|
```rust
|
|
use hashbrown::HashMap;
|
|
|
|
let mut map = HashMap::new();
|
|
map.insert(1, "one");
|
|
```
|
|
|
|
## Flags
|
|
|
|
This crate has the following Cargo features:
|
|
|
|
- `nightly`: Enables nightly-only features including: `#[may_dangle]`.
|
|
- `serde`: Enables serde serialization support.
|
|
- `rayon`: Enables rayon parallel iterator support.
|
|
- `equivalent`: Allows comparisons to be customized with the `Equivalent` trait.
|
|
(enabled by default)
|
|
- `raw-entry`: Enables access to the deprecated `RawEntry` API.
|
|
- `inline-more`: Adds inline hints to most functions, improving run-time
|
|
performance at the cost of compilation time. (enabled by default)
|
|
- `default-hasher`: Compiles with foldhash as default hasher. (enabled by
|
|
default)
|
|
- `allocator-api2`: Enables support for allocators that support
|
|
`allocator-api2`. (enabled by default)
|
|
|
|
## License
|
|
|
|
Licensed under either of:
|
|
|
|
* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
|
|
https://www.apache.org/licenses/LICENSE-2.0)
|
|
* MIT license ([LICENSE-MIT](LICENSE-MIT) or
|
|
https://opensource.org/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.
|