Elegantly determine if more than one boolean is “true”

Question

I have a set of five boolean values. If more than one of these are true I want to excecute a particular function. What is the most elegant way you can think of that would al

Answer 1

You mentioned

One interesting option is to store the booleans in a byte, do a right shift and compare with the original byte. Something like if (myByte && (myByte >> 1))

I don't think that expression will give you the result you want (at least using C semantics, since the expression is not valid C#):

If (myByte == 0x08), then the expression will return true even though there's only one bit set.

If you meant "if (myByte & (myByte >> 1))" then if (myByte == 0x0a) the expression will return false even though there are 2 bits set.

But here are some techniques for counting the number of bits in a word:

Bit Twiddling Hacks - Counting bits

A variation you might consider is to use Kernighan's counting method, but bail out early since you only need to know if there's more than one bit set:

int moreThanOneBitSet( unsigned int v)
{
    unsigned int c; // c accumulates the total bits set in v

    for (c = 0; v && (c <= 1); c++)
    {
      v &= v - 1; // clear the least significant bit set
    }

    return (c > 1);
}

Of course, using a lookup table's not a bad option either.