Auto merge of #207 - tkaitchuck:specialize, r=Amanieu

Enable specialization with aHash

This uses the specialization feature in nightly to improve performance for hashing some classes (u8, u16, u32, u64, u128, [u8], and String) For these classes it improves performance by 15% the test `insert_ahash` benchmarks.

Author: bors

Cargo.toml

@@ -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 }
@@ -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"

README.md

@@ -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).
@@ -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
 
@@ -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