Why bit shifting?

Question

I was recently looking at a config file that was saving some cryptic values. I happened to have the source available, so I took a look at what it was doing, and it was saving a bunch of different values and bit shifting them into each other. It mystified me why someone would do that. My question, then, is: is there an obvious advantage to storing numeric data in this way? I can see how it might make for a slightly smaller value to store, byte-wise, but it seems like a lot of work to save a couple of bytes of storage. It also seems like it would be significantly slower.

The other possibility that occurred to me is that is was used for obfuscation purposes. is this a common usage of bit shifting?

Answer 1

This is one of the common usages of bit shifting. There are several benefit:

1) Bit-shift operations are fast.

2) You can store multiple flags in a single value.

If you have an app that has several features, but you only want certain (configurable) ones enabled, you could do something like:

[Flags]
public enum Features
{
    Profile = 1,
    Messaging = 1 << 1,
    Signing = 1 << 2,
    Advanced = 1 << 3
}

And your single value to enable Messaging and Advanced would be:

(1 << 1) + (1 << 3) = 2 + 16 = 18

<add name="EnabledFeatures" value="18" />

And then to figure out if a given feature is enabled, you just perform some simple bitwise math:

var AdvancedEnabled = 
    EnabledFeatures & Features.Advanced == Features.Advanced;