How do you implement GetHashCode for structure with two string, when both strings are interchangeable

Question

I have a structure in C#:

public struct UserInfo
{
   public string str1
   {
     get;
     set;
   }

   public string str2
   {
     get;
     set;
   }           


        

Answer 1

GetHashCode's result is supposed to be:

1. As fast as possible.
2. As unique as possible.

Bearing those in mind, I would go with something like this:

if (str1 == null)
    if (str2 == null)
        return 0;
    else
       return str2.GetHashCode();
else
    if (str2 == null)
        return str1.GetHashCode();
    else
       return ((ulong)str1.GetHashCode() | ((ulong)str2.GetHashCode() << 32)).GetHashCode();

Edit: Forgot the nulls. Code fixed.