commit	6f1d4d46bfcd95ec7f7e9465ce157566ae72c1f0	[log] [tgz]
author	android-build-team Robot <android-build-team-robot@google.com>	Fri Feb 12 04:05:14 2021 +0000
committer	android-build-team Robot <android-build-team-robot@google.com>	Fri Feb 12 04:05:14 2021 +0000
tree	6e4d3b1c9ab986f8fbd8f58306ba38add67dd444
parent	c7aba54c01e63e1e6fa0586a9425b7c882991004 [diff]
parent	9147e79abb6f7614abe939a5c8c9fa1b03ccca62 [diff]

tree: 6e4d3b1c9ab986f8fbd8f58306ba38add67dd444

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.