The Fowler–Noll–Vo hash

The Fowler–Noll–Vo hash function is a simple but effective hash function. If you ever need to implement one from scratch, it is an excellent choice.

Note that this is not a cryptographic hash. It is intended to be used in hash tables and checksums.

The algorithm (or more precisely, the FNV-1a variant of the algorithm) is as follows:

#define FNV_OFFSET_BASIS 14695981039346656037
#define FNV_PRIME 1099511628211

uint64_t fnv_hash(uint8_t *data, size_t length) {
	uint64_t hash = FNV_OFFSET_BASIS;

	for (size_t i = 0; i < length; i++) {
		hash = hash ^ data[i];
		hash *= FNV_PRIME;
	}

	return hash;
}

This is the 64-bit variant. For other bit sizes, the size of the hash variable needs to be adapted and different constants need to be used for FNV_PRIME and FNV_OFFSET_BASIS:

References

FNV Hash by Landon Curt Noll, one of the authors of the FNV hash function.