Bug: 153120147

Clone this repo:
  1. bcc3cae Make rustc-hash available to product and vendor am: 114597b8d4 by Matthew Maurer · 3 weeks ago master
  2. 114597b Make rustc-hash available to product and vendor by Matthew Maurer · 3 weeks ago
  3. d3eb006 Update TEST_MAPPING am: 8a30e286de by Jeff Vander Stoep · 8 weeks ago
  4. 8a30e28 Update TEST_MAPPING by Jeff Vander Stoep · 8 weeks ago
  5. 631762c Merge "Update TEST_MAPPING" am: d09089c402 am: fda4ae1691 am: b9e389d827 am: 15c89bb590 by Treehugger Robot · 10 months ago main-16k-with-phones


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.