Microsoft messed up the 64 bit version of GetHashCode. This is a platform independent port of the 32 bit version of Object.GetHashCode based on the unsafe code of Yoni Toledano on StackOverflow (http://stackoverflow.com/a/835571/2132050)

GetHashCode32.cs

public static class StringExt
{
    public static int GetHashCode32(this string s)
    {
        var chars = s.ToCharArray();
        var lastCharInd = chars.Length - 1;
        var num1 = 0x15051505;
        var num2 = num1;
        var ind = 0;
        while (ind <= lastCharInd)
        {
            var ch = chars[ind];
            var nextCh = ++ind > lastCharInd ? '\0' : chars[ind];
            num1 = (((num1 << 5) + num1) + (num1 >> 0x1b)) ^ (nextCh << 16 | ch);
            if (++ind > lastCharInd) break;
            ch = chars[ind];
            nextCh = ++ind > lastCharInd ? '\0' : chars[ind++];
            num2 = (((num2 << 5) + num2) + (num2 >> 0x1b)) ^ (nextCh << 16 | ch);
        }
        return num1 + num2 * 0x5d588b65;
    }
}