1# rustc-hash 2 3[](https://crates.io/crates/rustc-hash) 4[](https://docs.rs/rustc-hash) 5 6A speedy, non-cryptographic hashing algorithm used by `rustc`. 7The [hash map in `std`](https://doc.rust-lang.org/std/collections/struct.HashMap.html) uses SipHash by default, which provides resistance against DOS attacks. 8These attacks aren't a concern in the compiler so we prefer to use a quicker, 9non-cryptographic hash algorithm. 10 11The original hash algorithm provided by this crate was one taken from Firefox, 12hence the hasher it provides is called FxHasher. This name is kept for backwards 13compatibility, but the underlying hash has since been replaced. The current 14design for the hasher is a polynomial hash finished with a single bit rotation, 15together with a wyhash-inspired compression function for strings/slices, both 16designed by Orson Peters. 17 18For `rustc` we have tried many different hashing algorithms. Hashing speed is 19critical, especially for single integers. Spending more CPU cycles on a higher 20quality hash does not reduce hash collisions enough to make the compiler faster 21on real-world benchmarks. 22 23## Usage 24 25This crate provides `FxHashMap` and `FxHashSet` as collections. 26They are simply type aliases for their `std::collection` counterparts using the Fx hasher. 27 28```rust 29use rustc_hash::FxHashMap; 30 31let mut map: FxHashMap<u32, u32> = FxHashMap::default(); 32map.insert(22, 44); 33``` 34 35### `no_std` 36 37The `std` feature is on by default to enable collections. 38It can be turned off in `Cargo.toml` like so: 39 40```toml 41rustc-hash = { version = "2.1", default-features = false } 42``` 43
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