| # rustc-hash |
| |
| [](https://crates.io/crates/rustc-hash) |
| [](https://docs.rs/rustc-hash) |
| |
| A speedy hash algorithm used within rustc. The hashmap in liballoc by |
| default uses SipHash which isn't quite as speedy as we want. In the |
| compiler we're not really worried about DOS attempts, so we use a fast |
| non-cryptographic hash. |
| |
| This is the same as the algorithm used by Firefox -- which is a |
| homespun one not based on any widely-known algorithm -- though |
| modified to produce 64-bit hash values instead of 32-bit hash |
| values. It consistently out-performs an FNV-based hash within rustc |
| itself -- the collision rate is similar or slightly worse than FNV, |
| but the speed of the hash function itself is much higher because it |
| works on up to 8 bytes at a time. |
| |
| ## Usage |
| |
| ```rust |
| use rustc_hash::FxHashMap; |
| |
| let mut map: FxHashMap<u32, u32> = FxHashMap::default(); |
| map.insert(22, 44); |
| ``` |
| |
| ### `no_std` |
| |
| This crate can be used as a `no_std` crate by disabling the `std` |
| feature, which is on by default, as follows: |
| |
| ```toml |
| rustc-hash = { version = "1.0", default-features = false } |
| ``` |
| |
| In this configuration, `FxHasher` is the only export, and the |
| `FxHashMap`/`FxHashSet` type aliases are omitted. |
