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SushiSean - 14 Oct 2007 22:36 GMT

I have some problems which getting bites.
For example 247 it is 11110111 in bytes.

int i = 247; // 11110111

How I can get some pozition on bite?
Something like this
i[0] = 1;
i[1] = 1;
i[2] = 1;
i[3] = 0;
i[4] = 1;
i[5] = 1;
i[6] = 1;
i[7] = 1;

So I can get 1 or 0 for any pozition.
i[2] = 1;
How I can do this?

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Arne Vajhøj - 14 Oct 2007 23:11 GMT

> I have some problems which getting bites.
> For example 247 it is 11110111 in bytes.
[quoted text clipped - 15 lines]
> i[2] = 1;
> How I can do this?

Welcome to the world of bit manipulation !

Try look at this code:

using System;

namespace E
{
    public class Program
    {
        public static void Main(string[] args)
        {
            byte v = 247;
            for(int i = 0; i < 8; i++)
            {
                Console.WriteLine(i + " " + ((v >> i) & 1));
            }
            Console.ReadKey();
        }
    }
}

Arne

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deerchao - 14 Oct 2007 23:14 GMT

On Oct 15, 6:11 am, Arne Vajh?j <a...@vajhoej.dk> wrote:

> > I have some problems which getting bites.
> > For example 247 it is 11110111 in bytes.
[quoted text clipped - 40 lines]
>
> Arne

Maybe it's a better idea to shift left but not right?
Because int is signed, sh.t right may expand the sign bit.

Reply to this Message

Arne Vajhøj - 14 Oct 2007 23:52 GMT

>> byte v = 247;
>> for(int i = 0; i < 8; i++)
>> {
>> Console.WriteLine(i + " " + ((v >> i) & 1));
>> }

> Maybe it's a better idea to shift left but not right?
> Because int is signed, sh.t right may expand the sign bit.

For this code it does not matter.

Arne

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Nicholas Paldino [.NET/C# MVP] - 15 Oct 2007 00:02 GMT

You can use the BitArray class, passing in the integer, like so:

BitArray bitArray = new BitArray(new int[]{i});

Now, bitArray[0] is equal to true, bitArray[3] is false, and so on, and
so on.

Signature

- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard.caspershouse.com

>I have some problems which getting bites.
> For example 247 it is 11110111 in bytes.
[quoted text clipped - 15 lines]
> i[2] = 1;
> How I can do this?

Reply to this Message

Michael C - 15 Oct 2007 04:14 GMT

> You can use the BitArray class, passing in the integer, like so:
>
> BitArray bitArray = new BitArray(new int[]{i});
>
> Now, bitArray[0] is equal to true, bitArray[3] is false, and so on, and
> so on.

This is potentially inefficient I guess. It's possibly better to just loop
through the bits using & and <<.

Michael

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Nicholas Paldino [.NET/C# MVP] - 15 Oct 2007 15:31 GMT

Michael,

"better" is a subjective term, at best. If you were to ask the OP, I
would say that using a BitArray is better, since it gives him the exact
functionality he is looking for.

Also, "potentially" inefficient doesn't hold much meaning. It probably
is slower than just applying a bit mask, but to be honest, I don't know how
much slower it can be and depending on what you are doing, how significant
that performance hit will be.

Signature

- Nicholas Paldino [.NET/C# MVP]
- mvp@spam.guard.caspershouse.com

>> You can use the BitArray class, passing in the integer, like so:
>>
[quoted text clipped - 7 lines]
>
> Michael

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Michael C - 16 Oct 2007 02:05 GMT

> Michael,
>
[quoted text clipped - 6 lines]
> how much slower it can be and depending on what you are doing, how
> significant that performance hit will be.

That is why I used the terms "potentially", "I guess" and "possibly".
Naturally it depends on the situation but it is wise to mention that your
solution is potentially inefficient. If used in a loop the BitConverter
could possibly be 50 to 100 times slower. (No I have not tested this and it
is a guesstimate).

Michael

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