生成不重复long型数字

传说这个方法可以生成20亿以内不重复long数值

  public long GetCode(string shardField)        {            uint code = 0;            shardField = shardField.Trim();            for (int i = 0; i < shardField.Length; i += 2)            {                code *= 16777619;                code ^= shardField[i];            }            var ss = code;            return ss;        }