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