Hash table design in libraries is an exercise in minimizing the costs of the worst case, and it's made harder by typically only being able to control one side o

Hash table design in libraries is an exercise in minimizing the costs of the worst case, and it's made harder by typically only being able to control one side of the equation - the table and not the hash function. Thus general purpose hash table implementations need to choose whether they will help naive programmers by doing modulus with a prime number of buckets, or if they will leave a potential performance bomb for people who e.g. hash integers to themselves. The article argues for a third way which is somewhere in the middle: faster than prime modulus, but not as dangerous as bit masking. It's usually easy to beat any general purpose hash table for these reasons, as long as you control the hash function you can tweak your implementation to suit.