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

First of all, consider using GetHashCode().

A simple improvement on your existing implementation:

static UInt64 CalculateHash(string read, bool lowTolerance)
{
    UInt64 hashedValue = 0;
    int i = 0;
    ulong multiplier = 1;
    while (i < read.Length)
    {
        hashedValue += read[i] * multiplier;
        multiplier *= 37;
        if (lowTolerance) i += 2;
        else i++;
    }
    return hashedValue;
}

It avoids the expensive floating point calculation, and the overhead of ElementAt.

Btw (UInt64)Math.Pow(31, i) doesn't work well for longer strings. Floating point rounding will lead to a multiplier of 0 for characters beyond 15 or so.