How do I calculate a good hash code for a list of strings?

Question

Background:

• I have a short list of strings.
• The number of strings is not always the same, but are nearly always of the order of a “handful”
• I

Answer 1

Using the GetHashCode() is not ideal for combining multiple values. The problem is that for strings, the hashcode is just a checksum. This leaves little entropy for similar values. e.g. adding hashcodes for ("abc", "bbc") will be the same as ("abd", "abc"), causing a collision.

In cases where you need to be absolutely sure, you'd use a real hash algorithm, like SHA1, MD5, etc. The only problem is that they are block functions, which is difficult to quickly compare hashes for equality. Instead, try a CRC or FNV1 hash. FNV1 32-bit is super simple:

public static class Fnv1 {
    public const uint OffsetBasis32 = 2166136261;
    public const uint FnvPrime32 = 16777619;

    public static int ComputeHash32(byte[] buffer) {
        uint hash = OffsetBasis32;

        foreach (byte b in buffer) {
            hash *= FnvPrime32;
            hash ^= b;
        }

        return (int)hash;
    }
}