Question

I have to create a hash function based on 3 shorts. What is the best way to go about doing this?

Edit
I have an object called Point. It is composed of three shorts (x, y, z). In order to use this object within a QSet, I have to fill in the body of the following function

uint qHash(const Point &point) {
    // return something here that is a unique combination of x, y, z so that
    // it is very quick to calculate and has minimal (if any) hash collisions
}

Answer 1

That depends a great deal on what you need from the hash function.

Is speed critical?

Is a near-perfect hash distribution critical?

How large must your hash key be? 32-bits? 64-bits? Larger?

Without knowledge of any other specifics, you may want to consider something along these lines:

uint hash = (31 * 31 * 31 * (uint)short1) ^ (31 * 31 * (uint)short2) ^ (31 * short3);

That will be fast and should have a reasonable distribution of bits, even if the input values for the shorts are not well distributed

UPDATE:

Modified code sample to type uint. My variant should work well if input is in the range 0 to 512.

If you’re interested in understanding why I multiply each input by a power of 31, see

Why does Java's hashCode() in String use 31 as a multiplier?