| commit | 5c19acf9825addf5a124ebab456c0848eaa4e5a0 | [log] [tgz] |
|---|---|---|
| author | Andrew Walbran <qwandor@google.com> | Thu Nov 09 16:25:13 2023 +0000 |
| committer | Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com> | Thu Nov 09 16:25:13 2023 +0000 |
| tree | 0526d3701991dddde3f39da6dc4fedb5e532af42 | |
| parent | d42802a455c0d50482dbe8b526cdd79c53b035f4 [diff] | |
| parent | 8ef599e7d67664aaa8faa246d0da28b8bba1a8a5 [diff] |
Migrate to cargo_embargo. am: 25ae9e30f0 am: e4842cafbd am: 8ef599e7d6 Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/fxhash/+/2822241 Change-Id: If2b7a31e1c49f68b7f73b2bf4edf0de2739afd19 Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
This hashing algorithm was extracted from the Rustc compiler. This is the same hashing algoirthm used for some internal operations in FireFox. The strength of this algorithm is in hashing 8 bytes at a time on 64-bit platforms, where the FNV algorithm works on one byte at a time.
It is not a cryptographically secure hash, so it is strongly recommended that you do not use this hash for cryptographic purproses. Furthermore, this hashing algorithm was not designed to prevent any attacks for determining collisions which could be used to potentially cause quadratic behavior in HashMaps. So it is not recommended to expose this hash in places where collissions or DDOS attacks may be a concern.
Building an Fx backed hashmap.
extern crate fxhash; use fxhash::FxHashMap; let mut hashmap = FxHashMap::new(); hashmap.insert("black", 0); hashmap.insert("white", 255);
Building an Fx backed hashset.
extern crate fxhash; use fxhash::FxHashSet; let mut hashmap = FxHashSet::new(); hashmap.insert("black"); hashmap.insert("white");
Generally fxhash is than fnv on u32, u64, or any byte sequence with length >= 5. However, keep in mind that hashing speed is not the only characteristic worth considering. That being said, Rustc had an observable increase in speed when switching from fnv backed hashmaps to fx based hashmaps.
bench_fnv_003 ... bench: 3 ns/iter (+/- 0) bench_fnv_004 ... bench: 2 ns/iter (+/- 0) bench_fnv_011 ... bench: 6 ns/iter (+/- 1) bench_fnv_012 ... bench: 5 ns/iter (+/- 1) bench_fnv_023 ... bench: 14 ns/iter (+/- 3) bench_fnv_024 ... bench: 14 ns/iter (+/- 4) bench_fnv_068 ... bench: 57 ns/iter (+/- 11) bench_fnv_132 ... bench: 145 ns/iter (+/- 30) bench_fx_003 ... bench: 4 ns/iter (+/- 0) bench_fx_004 ... bench: 3 ns/iter (+/- 1) bench_fx_011 ... bench: 5 ns/iter (+/- 2) bench_fx_012 ... bench: 4 ns/iter (+/- 1) bench_fx_023 ... bench: 7 ns/iter (+/- 3) bench_fx_024 ... bench: 4 ns/iter (+/- 1) bench_fx_068 ... bench: 10 ns/iter (+/- 3) bench_fx_132 ... bench: 19 ns/iter (+/- 5) bench_seahash_003 ... bench: 30 ns/iter (+/- 12) bench_seahash_004 ... bench: 32 ns/iter (+/- 22) bench_seahash_011 ... bench: 30 ns/iter (+/- 4) bench_seahash_012 ... bench: 31 ns/iter (+/- 1) bench_seahash_023 ... bench: 32 ns/iter (+/- 6) bench_seahash_024 ... bench: 31 ns/iter (+/- 5) bench_seahash_068 ... bench: 40 ns/iter (+/- 9) bench_seahash_132 ... bench: 50 ns/iter (+/- 12)