A fast hash function for string in C#

Question

I want to hash a string of length up-to 30. What will be the best idea to do that if time is my concern. The function will be called over 100 million times. currently I am u

Answer 1

To speed up your implementation, the (UInt64)Math.Pow(31, i) call should be replaced by a lookup: pre-calculate a table of the first 30 powers of 31, and use it at runtime. Since the limit on length is 30, you need only 31 element:

private static unsigned long[] Pow31 = new unsigned long[31];

static HashCalc() {
    Pow31[0] = 1;
    for (int i = 1 ; i != Pow31.Length ; i++) {
        Pow31[i] = 31*Pow31[i-1];
    }
}

// In your hash function...
hashedValue += read.ElementAt(i) * Pow31[i];