hash_hasher

A std::hash::Hasher which is designed to work with already-hashed or hash-like data.

Details

The provided hasher does minimal work under the assumption that the input data is already suitable for use as a key in a HashSet or HashMap.

As well as the performance benefit, it also causes HashSets or HashMaps to become somewhat deterministic. Given two equal HashSets or HashMaps containing more than a single element, iterating them will yield the elements in differing orders. By using a HashSet<_, HashBuildHasher> or HashMap<_, _, HashBuildHasher>, then if the same data is inserted and/or removed in the same order, iterating the collection will yield a consistent order.

Example

```rust extern crate hash_hasher;

use std::collections::HashMap; use hash_hasher::HashBuildHasher;

let hashbuilder = HashBuildHasher::default(); let mut map: HashMap = HashMap::withhasher(hash_builder);

assert!(map.insert(0, "zero").isnone()); assert!(map.insert(1024, "1024").isnone()); assert_eq!(Some("zero"), map.insert(0, "nothing")); ```

Benchmarks

A benchmark suite is included and sample figures can be found at the end of the AppVeyor results and the nightly jobs of the Travis results.

For example:

``` insertsha1sintosetusingdefaulthasher ... bench: 3,382 ns/iter (+/- 276) insertsha1sintosetusinghashhasher ... bench: 1,657 ns/iter (+/- 166)

insertsha256sintosetusingdefaulthasher ... bench: 4,002 ns/iter (+/- 374) insertsha256sintosetusinghashhasher ... bench: 1,523 ns/iter (+/- 82)

insertsha512sintosetusingdefaulthasher ... bench: 5,128 ns/iter (+/- 228) insertsha512sintosetusinghashhasher ... bench: 1,859 ns/iter (+/- 109)

insertsiphashesintosetusingdefaulthasher ... bench: 2,351 ns/iter (+/- 171) insertsiphashesintosetusinghashhasher ... bench: 630 ns/iter (+/- 13) ```

License

Licensed 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 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.