What's a good hash function for English words?

Question

I have a long list of English words and I would like to hash them. What would be a good hashing function? So far my hashing function sums the ASCII values of the letters then modulo the table size. I'm looking for something efficient and simple.

Answer 1

To simply sum the letters is not a good strategy because a permutation gives the same result.

This one (djb2) is quite popular and works nicely with ASCII strings.

unsigned long hashstring(unsigned char *str) {     unsigned long hash = 5381;     int c;      while (c = *str++)         hash = ((hash << 5) + hash) + c; /* hash * 33 + c */      return hash; } 

More info here.

If you need more alternatives and some perfomance measures, read here.

Added: These are general hashing functions, where the input domain is not known in advance (except perhaps some very general assumptions: eg the above works slightly better with ascii input), which is the most usual scenario. If you have a known restricted domain (set of inputs fixed) you can do better, see Fionn's answer.

Answer 2

Maybe something like this would help you: http://www.gnu.org/s/gperf/

It generates a optimized hashing function for the input domain.