| commit | 1d7c634b8a836ca4b7365698ef0c29d079da25b3 | [log] [tgz] |
|---|---|---|
| author | Chan Wang <[email protected]> | Thu Aug 22 08:15:37 2024 +0000 |
| committer | Chan Wang <[email protected]> | Thu Aug 22 08:24:27 2024 +0000 |
| tree | b5237b91dc34fbafb27fe4cb478158375d825799 | |
| parent | a913c921226d15e4ed7288f3a92a69fcf9832403 [diff] |
Mark "libfnv" available in our OEM APEXs In our project there would be a lot of OEM APEXs and we don't know their name so prefix is used as supported in aosp/3223005. We have library libsdv_comms_rs which depends on libhttp and libhttp depends on libfnv. Test: m Bug: 342346986 Change-Id: Ica1e04ddb16cc884ae6dbf65a863f04c2ce46ff1
An implementation of the Fowler–Noll–Vo hash function.
The FNV hash function is a custom Hasher implementation that is more efficient for smaller hash keys.
The Rust FAQ states that while the default Hasher implementation, SipHash, is good in many cases, it is notably slower than other algorithms with short keys, such as when you have a map of integers to other values. In cases like these, FNV is demonstrably faster.
Its disadvantages are that it performs badly on larger inputs, and provides no protection against collision attacks, where a malicious user can craft specific keys designed to slow a hasher down. Thus, it is important to profile your program to ensure that you are using small hash keys, and be certain that your program could not be exposed to malicious inputs (including being a networked server).
The Rust compiler itself uses FNV, as it is not worried about denial-of-service attacks, and can assume that its inputs are going to be small—a perfect use case for FNV.
To include this crate in your program, add the following to your Cargo.toml:
[dependencies] fnv = "1.0.3"
The FnvHashMap type alias is the easiest way to use the standard library’s HashMap with FNV.
use fnv::FnvHashMap; let mut map = FnvHashMap::default(); map.insert(1, "one"); map.insert(2, "two"); map = FnvHashMap::with_capacity_and_hasher(10, Default::default()); map.insert(1, "one"); map.insert(2, "two");
Note, the standard library’s HashMap::new and HashMap::with_capacity are only implemented for the RandomState hasher, so using Default to get the hasher is the next best option.
Similarly, FnvHashSet is a type alias for the standard library’s HashSet with FNV.
use fnv::FnvHashSet; let mut set = FnvHashSet::default(); set.insert(1); set.insert(2); set = FnvHashSet::with_capacity_and_hasher(10, Default::default()); set.insert(1); set.insert(2);