1# rustc-hash 2 3[](https://crates.io/crates/rustc-hash) 4[](https://docs.rs/rustc-hash) 5 6A speedy hash algorithm used within rustc. The hashmap in liballoc by 7default uses SipHash which isn't quite as speedy as we want. In the 8compiler we're not really worried about DOS attempts, so we use a fast 9non-cryptographic hash. 10 11This is the same as the algorithm used by Firefox -- which is a 12homespun one not based on any widely-known algorithm -- though 13modified to produce 64-bit hash values instead of 32-bit hash 14values. It consistently out-performs an FNV-based hash within rustc 15itself -- the collision rate is similar or slightly worse than FNV, 16but the speed of the hash function itself is much higher because it 17works on up to 8 bytes at a time. 18 19## Usage 20 21```rust 22use rustc_hash::FxHashMap; 23 24let mut map: FxHashMap<u32, u32> = FxHashMap::default(); 25map.insert(22, 44); 26``` 27 28### `no_std` 29 30This crate can be used as a `no_std` crate by disabling the `std` 31feature, which is on by default, as follows: 32 33```toml 34rustc-hash = { version = "1.0", default-features = false } 35``` 36 37In this configuration, `FxHasher` is the only export, and the 38`FxHashMap`/`FxHashSet` type aliases are omitted. 39
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