commit	4f45e0fc398bf478eb46030b89bb349fb1ceb89e	[log] [tgz]
author	android-build-team Robot <android-build-team-robot@google.com>	Fri Nov 06 02:09:48 2020 +0000
committer	android-build-team Robot <android-build-team-robot@google.com>	Fri Nov 06 02:09:48 2020 +0000
tree	5878d4e303f42d42e1b161d33f687332950fa3d7
parent	3c5bbd4e62fa0b68bd42ccda5f0543a82686415b [diff]
parent	97605a7ff4b67c34d83c3e267e164f2c5a5d4c06 [diff]

tree: 5878d4e303f42d42e1b161d33f687332950fa3d7

README.md

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

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.