commit	3c5bbd4e62fa0b68bd42ccda5f0543a82686415b	[log] [tgz]
author	android-build-team Robot <android-build-team-robot@google.com>	Tue Oct 13 01:06:40 2020 +0000
committer	android-build-team Robot <android-build-team-robot@google.com>	Tue Oct 13 01:06:40 2020 +0000
tree	b27942870d2193374ae2e1cb1fbaba4ddf9e6119
parent	bf1398b40df420e540701abead8f9810161c02f6 [diff]
parent	75f5a0c20ca1798f0c4c1fe41311fcdacbf208bf [diff]

tree: b27942870d2193374ae2e1cb1fbaba4ddf9e6119

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.