Bug: 153120147

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  1. dc437b0 Mark ab/6881855 as merged by Xin Li · 8 weeks ago master
  2. 6ef76c8 TEST_MAPPING: test dependers of this crate am: d0d1edece4 by Jeff Vander Stoep · 2 months ago
  3. d0d1ede TEST_MAPPING: test dependers of this crate by Jeff Vander Stoep · 3 months ago
  4. 0c11f43 Copy description from Cargo.toml to METADATA am: 7ca0635669 by Chih-Hung Hsieh · 3 months ago
  5. 7ca0635 Copy description from Cargo.toml to METADATA by Chih-Hung Hsieh · 3 months ago

rustc-hash

crates.io Documentation

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

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:

rustc-hash = { version = "1.0", default-features = false }

In this configuration, FxHasher is the only export, and the FxHashMap/FxHashSet type aliases are omitted.