https://github.com/n-r-k/chibihash
Small, Fast, Portable 64-bit hash function
https://github.com/n-r-k/chibihash
64-bit c hash hash-function hash-functions smhasher
Last synced: 28 days ago
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Small, Fast, Portable 64-bit hash function
- Host: GitHub
- URL: https://github.com/n-r-k/chibihash
- Owner: N-R-K
- Created: 2024-11-16T15:23:56.000Z (6 months ago)
- Default Branch: master
- Last Pushed: 2024-11-29T20:43:58.000Z (5 months ago)
- Last Synced: 2025-03-30T12:09:10.153Z (about 1 month ago)
- Topics: 64-bit, c, hash, hash-function, hash-functions, smhasher
- Language: C
- Homepage: https://nrk.neocities.org/articles/chibihash
- Size: 14.6 KB
- Stars: 115
- Watchers: 5
- Forks: 1
- Open Issues: 0
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Metadata Files:
- Readme: README.md
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README
# ChibiHash: Small, Fast 64 bit hash function
I started writing this because all the 64 bit hash functions I came across were
either too slow (FNV-1a, one byte at a time processing), or too large spanning
hundreds of lines of code, or non-portable due to using hardware specific
instructions.
Being small and portable, the goal is to be able to use ChibiHash as a good
"default" for non-cryptographic 64-bit hashing needs.
Some key features:
* Small: ~65 loc in C
* Fast: See benchmark table below
* Portable: Doesn't use hardware specific instructions (e.g SSE)
* Good Quality: Passes [smhasher][] and [smhasher3][], so should be good quality (I think)
* Unencumbered: Released into the public domain
* Free of undefined behavior and gives same result regardless of host system's endianness.
* Non-cryptographic
Here's some benchmark (made via smhasher3) against other similar themed hash functions:
| Name | Large input (GiB/sec) | Small input (Cycles/Hash) |
| :--- | :-------------------------: | :------------------------: |
| chibihash64 | **24.20** | 34 |
| xxhash64 | 15.10 | 50 |
| city64 | 18.30 | 47 |
| spooky64 | 16.68 | 70 |
| rapidhash.protected 1 | 21.50 | **32** |
| polymur-hash 1, 2 | 13.82 | 43 |
1. Requires compiler/cpu support for retrieving the full 128 bit result of a
64x64 bit multiply.
2. Universal, but has a complicated seeding step.
[smhasher]: https://github.com/aappleby/smhasher
[smhasher3]: https://gitlab.com/fwojcik/smhasher3
## When NOT to use
The introduction should make it clear on why you'd want to use this.
Here are some reasons to avoid using this:
* For cryptographic purposes.
* For protecting against [collision attacks](https://en.wikipedia.org/wiki/Collision_attack) (SipHash is the recommended one for this purpose).
* When you need very strong probability against collisions: ChibiHash does very
minimal amount of mixing compared to other hashes (e.g xxhash64). And so
chances of collision should in theory be higher.
## Unofficial ports
A list of unofficial ports to other languages is [maintained here](https://github.com/N-R-K/ChibiHash/issues/4).
## Changelog
### v2
- Faster performance on short string (42 cycles/hash vs 34 cycles/hash).
The tail end handling has been reworked entirely with some inspiration from
wyhash's short input reading.
- Better seeding. v1 seed only affected 64 bits of the initial state.
v2 seed affects the full 256 bits. This allows it to pass smhasher3's
SeedBlockLen and SeedBlockOffset tests.
- Slightly better mixing in bulk handling.
- Passes all 252 tests in smhasher3 (commit 34093a3), v1 failed 3.