ChibiHash: Small, Fast 64 bit hash function

See also: “Meow hash” by the legendary Casey Muratori, a fast non-cryptographic hash function: https://github.com/cmuratori/meow_hash

> It’s the fastest hash function we know of, and we have benchmarked all the ones we could find. On modern Intel x64 CPUs, it hashes 16 bytes per cycle single-threaded. This means in cache it can hash at a rate of 64 gigabytes per second on a 4.2gHz machine. Out of cache, it hashes at whatever speed your main memory bus can provide to a single core, since that is usually the limiting factor on modern x64 CPUs.

> It has also now been tuned to be the fastest hash on small inputs, too. Despite the fact that it is a full 128-bit hash, it still outperforms “fast” 64-bit hashes across all input sizes.

— https://archive.is/CQOVm (originally https://mollyrocket.com/meowhash)

Discussion on HN: https://news.ycombinator.com/item?id=29038813 & https://news.ycombinator.com/item?id=18262627

> See also: “Meow hash”

Meow hash may very well be fast on large data, but it completely fails the "small code" criteria, which is one of the clearly stated design goal of Chibi.

Generally speaking, the "code as small as possible" is IMO a design constraint that is very often under-estimated or even ignored for these type of algorithms, including the crypto hard ones.

I personally find the "code fits on half a page" metric very important: beyond satisfying some very personal sense of aesthetics, it buys you quite a lot of nice properties:

   - fits in head
   - inlines like a dream
   - easy to integrate
   - easy to do header only
   - easy to security audit
   - pretty hard to introduce bugs
   - nothing up my sleeve numbers pretty much obvious

For these reasons, I used to love the TEA (tiny encryption algorithm) [1] before cryptanalysis unfortunately showed it to be weak. Its successors (XXTEA, etc...) are already almost too big for my taste.

The speck cipher [2] is quite nice in that regard, in spite of its rather untrustworthy provenance.

[1] https://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm

[2] https://en.wikipedia.org/wiki/Speck_(cipher)