summaryrefslogtreecommitdiffstats
path: root/third_party/rust/hashbrown/README.md
diff options
context:
space:
mode:
Diffstat (limited to 'third_party/rust/hashbrown/README.md')
-rw-r--r--third_party/rust/hashbrown/README.md126
1 files changed, 126 insertions, 0 deletions
diff --git a/third_party/rust/hashbrown/README.md b/third_party/rust/hashbrown/README.md
new file mode 100644
index 0000000000..2eddcf3e29
--- /dev/null
+++ b/third_party/rust/hashbrown/README.md
@@ -0,0 +1,126 @@
+hashbrown
+=========
+
+[![Build Status](https://github.com/rust-lang/hashbrown/actions/workflows/rust.yml/badge.svg)](https://github.com/rust-lang/hashbrown/actions)
+[![Crates.io](https://img.shields.io/crates/v/hashbrown.svg)](https://crates.io/crates/hashbrown)
+[![Documentation](https://docs.rs/hashbrown/badge.svg)](https://docs.rs/hashbrown)
+[![Rust](https://img.shields.io/badge/rust-1.56.1%2B-blue.svg?maxAge=3600)](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 = "0.12"
+```
+
+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.
+- `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)
+- `bumpalo`: Provides a `BumpWrapper` type which allows `bumpalo` to be used for memory allocation.
+- `ahash`: Compiles with ahash as default hasher. (enabled by default)
+- `ahash-compile-time-rng`: Activates the `compile-time-rng` feature of ahash. For targets with no random number generator
+this pre-generates seeds at compile time and embeds them as constants. See [aHash's documentation](https://github.com/tkaitchuck/aHash#flags) (disabled 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.