Vendor things

third-party/vendor/rustc-hash/README.md

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+# rustc-hash
+
+[![crates.io](https://img.shields.io/crates/v/rustc-hash.svg)](https://crates.io/crates/rustc-hash)
+[![Documentation](https://docs.rs/rustc-hash/badge.svg)](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.