The big thing to note here is that it needs to be a power of two, so that the modulo operation on the hash table is really a mask operation, not a divide.  It's easy to tell the compiler that if it's a compile time constant.  Needs a lot more finesse if it's not.

But it could reasonably be configurable at compile time.  Just make sure to spit the dummy out if it's a weird size.

- Jonathan Morton