Thanks for mentioning this, I forgot to include this in my PR body. Yes this does increase the size of the `HashMap`. I did this from a suggestion by @pcwalton that it may be faster to initialize the SipState and just clone it for each value we hash. It's that classic cpu vs memory tradeoff. I'm happy to revert it. Now that we have hasher-generic-HashMaps, it's easy enough to make two `Hashers`, one being more memory-heavy, the other being more cpu-heavy, and let the user decide which would be better for them.