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:

Bits	FNV prime	FNV offset basis
32	16777619	2166136261
64	1099511628211	14695981039346656037
128	309485009821345068724781371	144066263297769815596495629667062367629
256	374144419156711147060143317 175368453031918731002211	100029257958052580907070968620625704837 092796014241193945225284501741471925557
512	358359158748448673689190764 890951084499463279557543925 583998256154206699388825751 26094039892345713852759	965930312949666949800943540071631046609 041874567263789610837432943446265799458 293219771643844981305189220653980578449 5328239340083876191928701583869517785
1024	501645651011311865543459881103 527895503076534540479074430301 752383111205510814745150915769 222029538271616265187852689524 938529229181652437508374669137 180409427187316048473796672026 0389217684476157468082573	14197795064947621068722070641403218320 88062279544193396087847491461758272325 22967323037177221508640965212023555493 65628174669108571814760471015076148029 75596980407732015769245856300321530495 71501574036444603635505054127112859663 61610267868082893823963790439336411086 884584107735010676915

References

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