C# Operators Bitwise

Question

I've been looking over some game programming code and have seen enums as in:

[Flags]
public enum CollisionCategories
{
    Cat1 = (1 << 0),
    Cat2 = (1 << 1),
    Cat3 = (1 << 2),
    Cat4 = (1 << 3),
    ...
}

Now, would this not be the same as just setting each item like 1, 2, 4, 8, ... ? I've seen the later as well. I know doing something like string s = string.Empty is better than string s = "" as far as performance goes but not sure about the enum.

Any thoughts?

Thanks much,

David

s = string.Empty is just more expressive that's why people are using it, this has nothing to do with performance — BrokenGlass
– BrokenGlass, Commented Jan 15, 2011 at 18:03
It is exactly the same thing... (1 << x) will be compiled to a constant so there is no performance differences. It is only because it might be easier to read (1 << 8) rather than 256. — Lasse Espeholt
– Lasse Espeholt, Commented Jan 15, 2011 at 18:04
I wish [flags] automagically gave you 1, 2, 4, 8, etc.... in place of 0, 1, 2, 3, ... rather than having to type it in manually. One can dream. — kenny
– kenny, Commented Jan 15, 2011 at 18:09

Mark Wilkins · Accepted Answer · 2011-01-15 18:03:56Z

3

You are correct about the values that are stored. It would not make a difference in performance, so it is a readability issue that may make more sense in the context of the code.

answered Jan 15, 2011 at 18:03

Mark Wilkins

41.3k5 gold badges61 silver badges111 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Yochai Timmer · Accepted Answer · 2011-01-15 18:04:58Z

1

It's just easier when you get to the larger numbers.

I'm sure that (1<< 24) is simpler than going to your calculator, calculating it, and pasting.

answered Jan 15, 2011 at 18:04

Yochai Timmer

49.6k25 gold badges154 silver badges191 bronze badges

Comments

SilverbackNet · Accepted Answer · 2011-01-15 18:05:10Z

1

For some people, setting them this way is just cleaner than the typical C raw hex/decimal number initialization. (0x1,0x4000,etc) Since the compiler recognizes a literal and turns them into plain numbers, there's no performance drawback, it's just a style matter.

answered Jan 15, 2011 at 18:05

SilverbackNet

2,07217 silver badges29 bronze badges

Comments

Al Kepp · Accepted Answer · 2011-01-15 18:04:27Z

0

Yes it is the same.

I personally would use 1,2,4,8... because I think these numbers are so much well known that no one can misunderstand what's going on.

Performance is the same. Code size is the same.

answered Jan 15, 2011 at 18:04

Al Kepp

5,9803 gold badges30 silver badges52 bronze badges

2 Comments

casablanca Over a year ago

Maybe the first few powers of 2 are well-known but those numbers get huge quite fast. If you have more than say 5 flags, the bit-shift representation is definitely more readable.

Al Kepp Over a year ago

Yes of course. I use only for small numbers, I remember values for 18 bits. Usually this is all I need when defining my enums.

Dan · Accepted Answer · 2011-01-15 18:04:47Z

0

Yes, it is the same. It's just so the code is more readable.

answered Jan 15, 2011 at 18:04

Dan

6,0624 gold badges41 silver badges78 bronze badges

Comments

James Gaunt · Accepted Answer · 2011-01-15 18:05:08Z

0

I think String.Empty is equivalent to "" the compiler will recognise the literal and convert it..... Anyway, it's the same for you enum, it's just a question of style and in the case of the enum it makes it 100% explicit that these are bit flags I suppose.

Or maybe the coder wasn't confident with his powers of 2, and couldn't be bothered to work them out.

answered Jan 15, 2011 at 18:05

James Gaunt

14.8k2 gold badges42 silver badges57 bronze badges

Comments

Aliostad · Accepted Answer · 2011-01-15 18:06:40Z

0

Performance is not an issue here. Enum is compiled as a constant so it is the compiler that is doing the job hence no difference in runtime performance.

Alternative could have been using the power but since that involves code, it would not work:

enum MyEnum{
  Val1 = Math.Pow(1,2) // throws compile error
}

Error 1 The expression being assigned to 'ConsoleApplication1.Program.MyEnum.Val1' must be constant C:\Users\Aliostad\Documents\Visual Studio 2010\Projects\ConsoleApplication1\ConsoleApplication1\Program.cs 130 11 ConsoleApplication1

Enum values must be constants.

answered Jan 15, 2011 at 18:06

Aliostad

81.9k21 gold badges164 silver badges209 bronze badges

Collectives™ on Stack Overflow

C# Operators Bitwise

7 Answers 7

Comments

Comments

Comments

2 Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

Comments

Comments

Comments

2 Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related