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diff --git a/third_party/rust/rustc-hash/README.md b/third_party/rust/rustc-hash/README.md new file mode 100644 index 0000000000..e33057ac8b --- /dev/null +++ b/third_party/rust/rustc-hash/README.md @@ -0,0 +1,38 @@ +# 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. |