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Enable specialization with aHash #207

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merged 16 commits into from
Dec 10, 2020
Merged

Enable specialization with aHash #207

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b5d8a69
Enable specialization with aHash
tkaitchuck Oct 12, 2020
71eaa19
Prevent some warnings and fix formatting
tkaitchuck Oct 12, 2020
67bf6b3
Use no-std by default.
tkaitchuck Oct 12, 2020
5563b42
PR feedback
tkaitchuck Oct 20, 2020
64c31fe
Fix warnings
tkaitchuck Oct 20, 2020
383ff52
Update aHash version to work around lack of atomics
tkaitchuck Oct 20, 2020
29f39aa
Update ahash version
tkaitchuck Oct 21, 2020
40e7e08
Change to aHash 0.6.1 and make key type explicet
tkaitchuck Nov 25, 2020
78ec552
Update benchmarks
tkaitchuck Nov 25, 2020
319b63f
Merge with master
tkaitchuck Nov 25, 2020
d5b5a1a
Minor cleanup
tkaitchuck Nov 25, 2020
5d07751
Cargo fmt
tkaitchuck Nov 25, 2020
1e4b95a
Clean up after merge.
tkaitchuck Nov 25, 2020
d9053f8
Fix build error
tkaitchuck Nov 25, 2020
62f60ed
Merge branch 'master' into specialize
tkaitchuck Dec 10, 2020
f1d3137
Clean up after merge
tkaitchuck Dec 10, 2020
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4 changes: 2 additions & 2 deletions Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,7 @@ edition = "2018"

[dependencies]
# For the default hasher
ahash = { version = "0.4.4", optional = true, default-features = false }
ahash = { version = "0.6.1", default-features = false, optional = true }

# For external trait impls
rayon = { version = "1.0", optional = true }
Expand All @@ -25,7 +25,7 @@ compiler_builtins = { version = "0.1.2", optional = true }
alloc = { version = "1.0.0", optional = true, package = "rustc-std-workspace-alloc" }

[dev-dependencies]
lazy_static = "1.2"
lazy_static = "1.4"
rand = { version = "0.7.3", features = ["small_rng"] }
rayon = "1.0"
fnv = "1.0.7"
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92 changes: 45 additions & 47 deletions README.md
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Expand Up @@ -26,7 +26,7 @@ in environments without `std`, such as embedded systems and kernels.
## Features

- Drop-in replacement for the standard library `HashMap` and `HashSet` types.
- Uses `AHash` as the default hasher, which is much faster than SipHash.
- Uses [AHash](https://github.com/tkaitchuck/aHash) as the default hasher, which is much faster than SipHash.
- 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).
Expand All @@ -37,47 +37,46 @@ in environments without `std`, such as embedded systems and kernels.

Compared to the previous implementation of `std::collections::HashMap` (Rust 1.35).

With the hashbrown default AHash hasher (not HashDoS-resistant):

```text
name oldstdhash ns/iter hashbrown ns/iter diff ns/iter diff % speedup
insert_ahash_highbits 20,846 7,397 -13,449 -64.52% x 2.82
insert_ahash_random 20,515 7,796 -12,719 -62.00% x 2.63
insert_ahash_serial 21,668 7,264 -14,404 -66.48% x 2.98
insert_erase_ahash_highbits 29,570 17,498 -12,072 -40.83% x 1.69
insert_erase_ahash_random 39,569 17,474 -22,095 -55.84% x 2.26
insert_erase_ahash_serial 32,073 17,332 -14,741 -45.96% x 1.85
iter_ahash_highbits 1,572 2,087 515 32.76% x 0.75
iter_ahash_random 1,609 2,074 465 28.90% x 0.78
iter_ahash_serial 2,293 2,120 -173 -7.54% x 1.08
lookup_ahash_highbits 3,460 4,403 943 27.25% x 0.79
lookup_ahash_random 6,377 3,911 -2,466 -38.67% x 1.63
lookup_ahash_serial 3,629 3,586 -43 -1.18% x 1.01
lookup_fail_ahash_highbits 5,286 3,411 -1,875 -35.47% x 1.55
lookup_fail_ahash_random 12,365 4,171 -8,194 -66.27% x 2.96
lookup_fail_ahash_serial 4,902 3,240 -1,662 -33.90% x 1.51
```

With the libstd default SipHash hasher (HashDoS-resistant):

```text
name oldstdhash ns/iter hashbrown ns/iter diff ns/iter diff % speedup
insert_std_highbits 32,598 20,199 -12,399 -38.04% x 1.61
insert_std_random 29,824 20,760 -9,064 -30.39% x 1.44
insert_std_serial 33,151 17,256 -15,895 -47.95% x 1.92
insert_erase_std_highbits 74,731 48,735 -25,996 -34.79% x 1.53
insert_erase_std_random 73,828 47,649 -26,179 -35.46% x 1.55
insert_erase_std_serial 73,864 40,147 -33,717 -45.65% x 1.84
iter_std_highbits 1,518 2,264 746 49.14% x 0.67
iter_std_random 1,502 2,414 912 60.72% x 0.62
iter_std_serial 6,361 2,118 -4,243 -66.70% x 3.00
lookup_std_highbits 21,705 16,962 -4,743 -21.85% x 1.28
lookup_std_random 21,654 17,158 -4,496 -20.76% x 1.26
lookup_std_serial 18,726 14,509 -4,217 -22.52% x 1.29
lookup_fail_std_highbits 25,852 17,323 -8,529 -32.99% x 1.49
lookup_fail_std_random 25,913 17,760 -8,153 -31.46% x 1.46
lookup_fail_std_serial 22,648 14,839 -7,809 -34.48% x 1.53
```
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

Expand All @@ -96,19 +95,18 @@ 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: `#[may_dangle]`.
- `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)
- `ahash`: Compiles with ahash as default hasher. (enabled by default)
- `ahash-compile-time-rng`: Activates the `compile-time-rng` feature of ahash, to increase the
DOS-resistance, but can result in issues for `no_std` builds. More details in
[issue#124](https://github.com/rust-lang/hashbrown/issues/124). (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

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