Bug: 153120147

Clone this repo:
  1. a0d91f2 Import 'rustc-hash' package version 1.1.0 am: adb9edf32a by Chih-Hung Hsieh · 7 weeks ago master
  2. adb9edf Import 'rustc-hash' package version 1.1.0 by Chih-Hung Hsieh · 8 weeks ago sdk-release platform-tools-30.0.0
  3. 1957306 Initial empty repository by Inna Palant · 9 weeks ago


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.


use rustc_hash::FxHashMap;

let mut map: FxHashMap<u32, u32> = FxHashMap::default();
map.insert(22, 44);


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.