FYI, we ended up implementing a _really_ nice SWAR version in the Carbon derivative of SwissTable that might be worth looking at for inspiration: https://github.com/carbon-language/carbon-lang/blob/trunk/co...

Can see the rest of that file and the adjacent `raw_hashtable.h` for the rest of the SwissTable-like implementation and `hashing.h` for the hash function.

FWIW, it consistently out-performs SwissTable in some respects, but uses a weaker but faster hash function that is good enough for the hash table, but not good for other use cases.