using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    [Flags]

    public enum TestEnum

    {

        None = 0,

        AA = 1,

        BB = 2,

        CC = 4,

        DD = 8,

    }

​

    public static IEnumerable<T> EnumerateMask<T>(Enum mask)

    {

        return Enum.GetValues(typeof (T)).Cast<Enum>().Where(mask.HasFlag).Cast<T>().Skip(1);

    }

​

    public static void Main()

    {

        var mask = TestEnum.AA | TestEnum.None | TestEnum.DD;

        foreach (var value in EnumerateMask<TestEnum>(mask))

        {

            Console.WriteLine(value);

        }

    }

}