Smash

smash is yet another blazingly fast hashmap written in Rust. smash makes use of Robin Hood hashing and the fxhash algorithm to achieve performance within a similar ballpark to the fastest existing hashmaps.

Using smash

smash is not currently hosted on crates.io due to its early development status.

Performance

Here are some benchmarks demonstrating the performance of smash compared to existing hashmaps. Each value is in nanoseconds, although the unit isn't relevant. For each test, I've also indicated what position smash comes in the rankings, along with how much faster/slower it is when compared to the best existing hashmap.

| Test            |       std |  fxhash | hashbrown |   smash(fx) | # | speedup |
--------------------------------------------------------------------------------|
| creation        |        10 |      12 |         3 |          10 | 2 |   - 17% |
| get existing    |   297,271 |  78,504 |    64,675 |      39,295 | 1 |   + 39% |
| get nonexistent |   320,710 |  59,314 |    36,457 |      57,751 | 2 |   - 58% |
| insert          | 1,081,676 | 542,295 |   267,689 |     167,045 | 1 |   + 38% |
| remove          |   427,348 | 172,378 |   138,499 |     130,205 | 1 |   +  6% |
| iterate keys    |    38,808 |  15,360 |    31,946 |      14,752 | 1 |   +  4% |
| iterate values  |    39,318 |  15,371 |    29,442 |      20,229 | 2 |   - 32% |

A Note On Hash Functions

smash uses the fxhash algorithm to compute hashes. fxhash, although faster than std's default hashing function, is not cryptographically secure. Like hashbrown, and std + fxhash, it is possible for an attacker to design hashmap keys that produce significantly worse performance when using smash than the benchmarks above.

When should I use smash?

At the moment, never.

smash is still under heavy development and isn't ready for production code. It's likely that it still has incorrectness bugs. That said, I'd appreciate testers to report issues very much.

However, based on current benchmarks, it's looking likely that smash might become a good choice in the following situations:

• When you need rapid access times for existing elements

• When you need to insert a lot of items into your hashmap

• When you need to remove a lot of items from your hashmap

smash is probably not such a good choice in the following situations:

• When you need to check whether a particular key exists within your hashmap a lot

Future

Future plans for smash include:

• A code cleanup

• A richer API that goes beyond that which is provided by std's hashmap

• More tests!

• Algorithm improvements

License

smash is distributed under either of:

• Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)

• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at the disgression of the user.