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My BitArray Class

, 12 Jun 2006
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A BitArray class with more function

Introduction

There's a BitArray class in namespace System.Collections.BitArray. But there's a big problem in it.

if you define two bytes as:

byte[] bits = new byte[2];
bits[0] = 1;
bits[1] = 3;

And use them in constructor of BitArray class, the bits must be "0000000100000011" because the byte[0] is "00000001"(binary view of 1) and the byte[1] is "00000011"(binary view of 3). Constructor first must use the first byte and then use the second byte.

But it won't !

The bits in the BitArray class will be "100000001100000". as you can see, the constructor first inverse each byte and then use it. and if you inverse all bits you gain "0000001100000001" wich that's not what we want.

Why ?

As i understood the problem come from CPU ! i wrote a thread in MSDN forum <!-- Article Starts - DO NOT ADD HTML/BODY START TAGS-->http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=466424&SiteID=1. i understood most of our cpu works little-endian (thank's nobugz in MSDN forum) it means they inverse bits.

for example if you send "00000001" to cpu it will store it in ram as "10000000" and when you read it cpu inverse it again and show you "00000001".

so our problem occur when we send "00000001" to cpu, cpu store it in ram as "10000000" and when we want the first bit the cpu return "1".

i think this problem occur in the constructor of System.Collections.BitArray. BitArray class must define a pointer to the first bit of array and start reading bits from there.

The program below show the problem. first it store 1 and 3 in two bytes. then use byte array for constructor. and show you a messagebox contain bits. it's not bad to change byte to int and 16 to 64 to see how problem will change. the constructor will inverse every 32 bits of data (int length)

byte[] bits = new byte[2];
bits[0] = 1;
bits[1] = 3;
BitArray BA = new BitArray(bits);
string st = string.Empty;
for(int i=0; i< 16; i++)
  st += Convert.ToInt16(BA.Get(i)).ToString();
MessageBox.Show(st); //source don't contain this test program

My BitArray Class

So i started to write my own bit array class. not even solve this problem also add more functions to it.

Inheritance Problem

First i want to write class that inherits from System.Collections.BitArray. but i don't know why microsoft defined BitArray class as a Sealed( notInheritable) class.

So i declared a ArrayList and store my bits in it. i have tried to my class be similar to BitArray class.

How it work's

I show an example of how my constructor work's for a byte array as an argument:

for each byte in array use Convert.ToString(TheByte,2). this function convert the byte to binary string. if our first byte be 43 this function return "101011". as you can see it's only 6 bit length. for store in our array a byte must be 8 bits length. so we call FixLength function to solve length problem. FixLength add two zero at the begining. and return "00101011"

Now we can add "00101011" to our array. we do this by calling AddBits function. this function add "false" to arrayList for each 0 and add "true" to arrayList for each 1 

public JIBitArray(byte[] bits)
{
  string st;
  foreach(byte b in bits)
  {
    st = FixLength(Convert.ToString(b,2),8);
    AddBits(st);
  }
}
private string FixLength(string num,int length)
{
  while(num.Length < length)
    num = num.Insert(0,"0");
  return num;
}<FONT size=2>
private void AddBits(string bits)
{
  foreach(char ch in bits)
  {
    if(ch == '0')
      _Bits.Add(false);
    else if(ch == '1')
      _Bits.Add(true);
    else
      throw(new ArgumentException("bits Contain none 0 1 character"));
  }
}<FONT size=2>

we do the same for other constructors.

Functions

i have defined Get, Set, SetAll, Count, Or, Xor, And, Not functions to do the same as Microsoft BitArray class do

And add more functions:

1. ShiftLeft, ShiftRight for shifting bits to left or right

To shift left simply remove bits from left and then add 0 bits to the end

2. GetLong, GetInt, GetByte, GetShort

This functions use to convert our bits to Long Array, Int Array Byte Array and Short Array

I explain one of them:

GetByte

we need to calculate return array length. To do this:

int</FONT> ArrayBound = (int)Math.Ceiling((double)this._Bits.Count/8);

Then declare array for returning:

byte[] Bits = new byte[ArrayBound];

if out array lenght be 9 bits. we need to return byte array with length of 2. so the array bound will be 2 and it means the lenght of array must be 16 bits. for fixing the length of our array we declare Temp JIBitArray and Fix it length to ArrayBound * ByteLength(which is 8)

JIBitArray Temp = new JIBitArray();
Temp._Bits = this._Bits;
Temp = FixLength(Temp,ArrayBound * 8);

Convert each 8 bits block to a byte by using "Convert.ToByte(string,base)" function.

<FONT color=#0000ff size=2><P>for</FONT><FONT size=2>(</FONT><FONT color=#0000ff size=2>int</FONT><FONT size=2> i=0; i< Temp._Bits.Count; i += 8)</P><P>{</P><P>  Bits[i/8] = Convert.ToByte(Temp.SubJIBitArray(i,8).ToString(),2);</P><P>}</P></FONT>

And then return bits.

3. RemoveBeginingZeros

if you have JIBitArray contain "00001110101" RemoveBeginingZeros return "110101"

4. operators

i have declared operator functions for this class

& And, | Or, ^ Xor, >> ShiftRight, << ShiftLeft

5. SubJIBitArray

it works like SubString function for string class. SubJIBitArray(2,3) for "0110110101" return "101"

License

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About the Author

Hamed J.I
Web Developer
Iran (Islamic Republic Of) Iran (Islamic Republic Of)
I began programming with C/C++ when i was 15. Then try to learn VC++ but at the middle of my reading .NET came.
 
I began to read C# and VB.NET and also began designing basic websites by FrontPage and developed some websites for our school and some other companis.
 
Later learn Microcontroller and design some digital circuits with PIC microcontrollers for a industrial controller company.
 
As I learned SQL and ASP.NET developed some website such as news portals that are active now.
 
Now i'm a software student and teach programming in computer institues. And have my own job by getting projects from companies.

Comments and Discussions

 
GeneralProblem with And method PinmemberMember 187509017-Mar-08 4:00 
Generalslow performance PinmemberZronZ7-Jan-07 23:08 
GeneralRe: slow performance [modified] Pinmemberyianfang28-Aug-07 16:51 
NewsThis guy saved my job!!!!! PinmemberPeace2u20-Jun-06 21:44 
GeneralRe: This guy saved my job!!!!! PinmemberHamed_ji31-Jul-06 13:24 
GeneralPretty redundant data type PinmemberAlexey A. Popov13-Jun-06 1:47 
GeneralRe: Pretty redundant data type PinmemberHamed_ji13-Jun-06 6:18 
GeneralRe: Pretty redundant data type Pinmemberreflex@codeproject13-Jun-06 7:10 
GeneralRe: Pretty redundant data type PinmemberHamed_ji13-Jun-06 8:51 
GeneralRe: Pretty redundant data type PinmemberAlexey A. Popov13-Jun-06 8:33 
GeneralRe: Pretty redundant data type PinmemberHamed_ji13-Jun-06 9:40 
AnswerRe: Pretty redundant data type PinmemberDrazen Dotlic14-Jun-06 1:34 
AnswerRe: Pretty redundant data type PinmemberHamed_ji31-Jul-06 13:22 
AnswerRe: Pretty redundant data type PinmemberDrazen Dotlic31-Jul-06 22:20 
Hamed_ji wrote:
you give 2 byte (as byte array) to BitArray class first byte is 00000000 and the second is 00000001. WHY when you get item number 9 it's 1 ? is it true order of bits ?
the BitOrder will contain 0000000010000000 IS IT EQUAL TO 0000000000000001 ?
 
if you give integer array to BitArray class it will inverse every 32 bits of order. Is it true Order ?
 
explain me what's the problem here ?. WHY the BitArray class inverse them.
 
let me know how you have used BitArray class in your BitTorrent project.

 
The reason you are surprised is because you are expecting to see an internal representation of ints (that are storage for the bits in the BitArray internally) the way you would like them to be.
 
But it's just that - internal representation. As we've said numerous times, the only time when you care about that is when you send BitArray over the wire, and in that context everything works fine.
 
There is no inversion. BitArray can store bits any way it likes. It is the class interface that you should use, and I don't see any inconsistencies there.
 
I've used BitArray to track which pieces of the "file" are available at each peer and to track my own too.
 
Hamed_ji wrote:
after all as i have said before. it's not slower than BitArray class because it's working with ArrayList and array list as our friend mentioned work with Pointers.
 
and i think a bad class that work true is better than any good class that inverse every 32bit (OR 8 bits) of data
 
i don't know if there's other resource that available about this problem. if it's please let me know them
 
And my advice to you. some times test the problems, find a way to solving them, and then write your message

 
It is slower. There are no pointers involved. There is boxing. All of this has been stated before. Have you checked if any of these claims is true?
 
Bad class is just bad. It does not matter if it "works", because in that sense BitArray works too. There is no problem.
 
If you still think this makes no sense, I have nothing more to add. Just check the MSDN documentation on all the points given above (especially by Aleksey).
 
Bring It On

GeneralRe: Pretty redundant data type PinmemberHamed_ji1-Aug-06 0:22 
GeneralRe: Pretty redundant data type PinmemberAlexey A. Popov14-Jun-06 7:25 

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