Counting the number of flags set on an enumeration

Question

I'm sure there must be a much better way of doing this. I'm trying to do a count operation on a Flags enum. Before I was itterating over all the possible values and counting the succesful AND operations.

e.g.

[Flags] public enum Skills {     None = 0,     Skill1 = 1,     Skill2 = 2,     Skill3 = 4,     Skill4 = 8,     Skill5 = 16,     Skill6 = 32,     Skill7 = 64,     Skill8 = 128 }  public static int Count(Skills skillsToCount) {    Skills skill;    for (int i = 0; i < SkillSet.AllSkills.Count; i++)    {       skill = SkillSet.AllSkills[i];       if ((skillsToCount & skill) == skill && skill != Skills.None)          count++;    }    return count; } 

I'm sure there must be a better way of doing this though, but must be suffering from a mental block. Can anyone advise a nicer solution?

Answer 1

The following code will give you the number of bits that are set for a given number of any type varying in size from byte up to long.

public static int GetSetBitCount(long lValue) {   int iCount = 0;    //Loop the value while there are still bits   while (lValue != 0)   {     //Remove the end bit     lValue = lValue & (lValue - 1);      //Increment the count     iCount++;   }    //Return the count   return iCount; } 

This code is very efficient as it only iterates once for each bit rather than once for every possible bit as in the other examples.