| 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, this is now the `HashMap` implementation for the Rust standard |
| library. 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 [AHash](https://github.com/tkaitchuck/aHash) as the default hasher, which is much faster than SipHash. |
| However, AHash 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. |
| |
| ## Performance |
| |
| Compared to the previous implementation of `std::collections::HashMap` (Rust 1.35). |
| |
| With the hashbrown default AHash hasher: |
| |
| | name | oldstdhash ns/iter | hashbrown ns/iter | diff ns/iter | diff % | speedup | |
| | :-------------------------- | :----------------: | ----------------: | :----------: | ------: | ------- | |
| | insert_ahash_highbits | 18,865 | 8,020 | -10,845 | -57.49% | x 2.35 | |
| | insert_ahash_random | 19,711 | 8,019 | -11,692 | -59.32% | x 2.46 | |
| | insert_ahash_serial | 19,365 | 6,463 | -12,902 | -66.63% | x 3.00 | |
| | insert_erase_ahash_highbits | 51,136 | 17,916 | -33,220 | -64.96% | x 2.85 | |
| | insert_erase_ahash_random | 51,157 | 17,688 | -33,469 | -65.42% | x 2.89 | |
| | insert_erase_ahash_serial | 45,479 | 14,895 | -30,584 | -67.25% | x 3.05 | |
| | iter_ahash_highbits | 1,399 | 1,092 | -307 | -21.94% | x 1.28 | |
| | iter_ahash_random | 1,586 | 1,059 | -527 | -33.23% | x 1.50 | |
| | iter_ahash_serial | 3,168 | 1,079 | -2,089 | -65.94% | x 2.94 | |
| | lookup_ahash_highbits | 32,351 | 4,792 | -27,559 | -85.19% | x 6.75 | |
| | lookup_ahash_random | 17,419 | 4,817 | -12,602 | -72.35% | x 3.62 | |
| | lookup_ahash_serial | 15,254 | 3,606 | -11,648 | -76.36% | x 4.23 | |
| | lookup_fail_ahash_highbits | 21,187 | 4,369 | -16,818 | -79.38% | x 4.85 | |
| | lookup_fail_ahash_random | 21,550 | 4,395 | -17,155 | -79.61% | x 4.90 | |
| | lookup_fail_ahash_serial | 19,450 | 3,176 | -16,274 | -83.67% | x 6.12 | |
| |
| |
| With the libstd default SipHash hasher: |
| |
| | name | oldstdhash ns/iter | hashbrown ns/iter | diff ns/iter | diff % | speedup | |
| | :------------------------ | :----------------: | ----------------: | :----------: | ------: | ------- | |
| | insert_std_highbits | 19,216 | 16,885 | -2,331 | -12.13% | x 1.14 | |
| | insert_std_random | 19,179 | 17,034 | -2,145 | -11.18% | x 1.13 | |
| | insert_std_serial | 19,462 | 17,493 | -1,969 | -10.12% | x 1.11 | |
| | insert_erase_std_highbits | 50,825 | 35,847 | -14,978 | -29.47% | x 1.42 | |
| | insert_erase_std_random | 51,448 | 35,392 | -16,056 | -31.21% | x 1.45 | |
| | insert_erase_std_serial | 87,711 | 38,091 | -49,620 | -56.57% | x 2.30 | |
| | iter_std_highbits | 1,378 | 1,159 | -219 | -15.89% | x 1.19 | |
| | iter_std_random | 1,395 | 1,132 | -263 | -18.85% | x 1.23 | |
| | iter_std_serial | 1,704 | 1,105 | -599 | -35.15% | x 1.54 | |
| | lookup_std_highbits | 17,195 | 13,642 | -3,553 | -20.66% | x 1.26 | |
| | lookup_std_random | 17,181 | 13,773 | -3,408 | -19.84% | x 1.25 | |
| | lookup_std_serial | 15,483 | 13,651 | -1,832 | -11.83% | x 1.13 | |
| | lookup_fail_std_highbits | 20,926 | 13,474 | -7,452 | -35.61% | x 1.55 | |
| | lookup_fail_std_random | 21,766 | 13,505 | -8,261 | -37.95% | x 1.61 | |
| | lookup_fail_std_serial | 19,336 | 13,519 | -5,817 | -30.08% | x 1.43 | |
| |
| ## Usage |
| |
| Add this to your `Cargo.toml`: |
| |
| ```toml |
| [dependencies] |
| hashbrown = "0.14" |
| ``` |
| |
| 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. |
| - `rkyv`: Enables rkyv serialization support. |
| - `rayon`: Enables rayon parallel iterator support. |
| - `raw`: Enables access to the experimental and unsafe `RawTable` API. |
| - `inline-more`: Adds inline hints to most functions, improving run-time performance at the cost |
| of compilation time. (enabled by default) |
| - `ahash`: Compiles with ahash 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/licenses/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. |
