Using bitwise operators

Question

I\'ve been studying C# and ran accross some familiar ground from my old work in C++. I never understood the reason for bitwise operators in a real application. I\'ve never u

Answer 1

Except for combining flags, bit logic isn't necessarily something you need in your UI code, but it is still tremendously important. For example, I maintain a binary serialization library, that needs to deal with all sorts of complex bit-packing strategies (variant length base-128 integer encoding, for example). This is one of the implementations (actually, this is a slower/safer version - there are other variants for dealing with buffered data, but they are harder to follow):

    public static bool TryDecodeUInt32(Stream source, out uint value)
    {
        if (source == null) throw new ArgumentNullException("source");

        int b = source.ReadByte();
        if (b < 0)
        {
            value = 0;
            return false;
        }

        if ((b & 0x80) == 0)
        {
            // single-byte
            value = (uint) b;
            return true;
        }

        int shift = 7;

        value = (uint)(b & 0x7F);
        bool keepGoing;
        int i = 0;
        do
        {
            b = source.ReadByte();
            if (b < 0) throw new EndOfStreamException();
            i++;
            keepGoing = (b & 0x80) != 0;
            value |= ((uint)(b & 0x7F)) << shift;
            shift += 7;
        } while (keepGoing && i < 4);
        if (keepGoing && i == 4)
        {
            throw new OverflowException();
        }
        return true;
    }

We have:

• tests to see if the most-significant-bit is set (this changes the meaning of the data)
• shifts-a-plenty
• removal of the most-significant-bit
• bitwise combination of values

This is real code, used in a real (and much used) protocol. In general, bit operations are used a lot in any kind of encoding layer.

It is also hugely important in graphics programming, for example. And lots of others.

There are also some micro-optimisations (maths intensive work etc) that can be done with bit operations.