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: ~60 loc in C
• Fast: See benchmark table below
• Portable: Doesn't use hardware specific instructions (e.g SSE)
• Good Quality: Passes smhasher, 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 against other similar hash functions:

It's the fastest of the bunch for large string throughput. For small string (< 32 bytes), cityhash beats it - worth noting that cityhash has hardcoded special cases for input below or equal 32 bytes.

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 (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.