31 releases

0.11.2 Mar 25, 2021
0.10.0 Jan 16, 2021
0.9.1 Sep 28, 2020
0.8.1 Jul 16, 2020
0.1.6 Nov 16, 2018

#1 in Data structures

Download history 177809/week @ 2020-12-23 217580/week @ 2020-12-30 295534/week @ 2021-01-06 282585/week @ 2021-01-13 311939/week @ 2021-01-20 310692/week @ 2021-01-27 312235/week @ 2021-02-03 317232/week @ 2021-02-10 361368/week @ 2021-02-17 349819/week @ 2021-02-24 337552/week @ 2021-03-03 354670/week @ 2021-03-10 353791/week @ 2021-03-17 382353/week @ 2021-03-24 363135/week @ 2021-03-31 332227/week @ 2021-04-07

1,326,224 downloads per month
Used in 8,571 crates (261 directly)

Apache-2.0/MIT

405KB
7.5K SLoC

hashbrown

Build Status Crates.io Documentation Rust

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.

Change log

Features

  • Drop-in replacement for the standard library HashMap and HashSet types.
  • Uses 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:

[dependencies]
hashbrown = "0.11"

Then:

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 (disabled by default)

License

Licensed under either of:

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.

Dependencies

~110–700KB
~14K SLoC