Persistent hashcode for strings [duplicate]

Answer 1

There is no built in, cross version stable, way to get a hash code of a string.

You could just copy the existing GetHashCode() code but exclude the portion that adds the build number as the seed and don't use unsafe calls to keep yourself safe from implementation detail changes.

Here is a fully managed version of the 64bit GetHashCode() that does not use any randomization and will return the same value for all future versions of .NET (as long as the behavior of int ^ char never changes).

public static class StringExtensionMethods
{
    public static int GetStableHashCode(this string str)
    {
        unchecked
        {
            int hash1 = 5381;
            int hash2 = hash1;

            for(int i = 0; i < str.Length && str[i] != '\0'; i += 2)
            {
                hash1 = ((hash1 << 5) + hash1) ^ str[i];
                if (i == str.Length - 1 || str[i+1] == '\0')
                    break;
                hash2 = ((hash2 << 5) + hash2) ^ str[i+1];
            }

            return hash1 + (hash2*1566083941);
        }
    }
}