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Posted 12 Jun 2006

My BitArray Class

, 12 Jun 2006
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A BitArray class with more function


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--> 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);
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')
    else if(ch == '1')
      throw(new ArgumentException("bits Contain none 0 1 character"));
}<FONT size=2>

we do the same for other constructors.


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:


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"


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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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.

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Comments and Discussions

GeneralProblem with And method Pin
Member 187509017-Mar-08 3:00
memberMember 187509017-Mar-08 3:00 
Generalslow performance Pin
ZronZ7-Jan-07 22:08
memberZronZ7-Jan-07 22:08 
GeneralRe: slow performance [modified] Pin
yianfang28-Aug-07 15:51
memberyianfang28-Aug-07 15:51 
NewsThis guy saved my job!!!!! Pin
Peace2u20-Jun-06 20:44
memberPeace2u20-Jun-06 20:44 
GeneralRe: This guy saved my job!!!!! Pin
Hamed_ji31-Jul-06 12:24
memberHamed_ji31-Jul-06 12:24 
GeneralPretty redundant data type Pin
Alexey A. Popov13-Jun-06 0:47
memberAlexey A. Popov13-Jun-06 0:47 
GeneralRe: Pretty redundant data type Pin
Hamed_ji13-Jun-06 5:18
memberHamed_ji13-Jun-06 5:18 
GeneralRe: Pretty redundant data type Pin
reflex@codeproject13-Jun-06 6:10
memberreflex@codeproject13-Jun-06 6:10 
GeneralRe: Pretty redundant data type Pin
Hamed_ji13-Jun-06 7:51
memberHamed_ji13-Jun-06 7:51 
GeneralRe: Pretty redundant data type Pin
Alexey A. Popov13-Jun-06 7:33
memberAlexey A. Popov13-Jun-06 7:33 
GeneralRe: Pretty redundant data type Pin
Hamed_ji13-Jun-06 8:40
memberHamed_ji13-Jun-06 8:40 
AnswerRe: Pretty redundant data type Pin
Drazen Dotlic14-Jun-06 0:34
memberDrazen Dotlic14-Jun-06 0:34 
Hamed_ji wrote:
perhaps in transfering data it don't make mistake. you send/recieve BYTES (i don't know what will occur if sender cpu be little-endian and the reciver be big-endian and it's not connect to my article ) and in transfering data we often work on BYTES not BITS. So what's the usage of BitArray class in transfering data ? i don't know if it's usefull. BitArray class is for working with bits so the bit order is important

There is no problem when transferring data, because there is network byte order which is fixed and not dependent on the processor's architecture (otherwise communicating between different platforms would be a major PITA).

As one of the previous posters mentioned, BitArray is a fine class that works exactly the way you'd expect (assuming you've read the documentation). I've used it in my BitTorrent implementation for the reasons one of the posters mentioned and have not had any problems with it.

But that's not the point. Your class is redundant, badly written, slow, and a classic example of "not invented here" syndrome. My advice to you is to embrace and accept the FCL and only write code that deals with your problem space...

Bring It On
AnswerRe: Pretty redundant data type Pin
Hamed_ji31-Jul-06 12:22
memberHamed_ji31-Jul-06 12:22 
AnswerRe: Pretty redundant data type Pin
Drazen Dotlic31-Jul-06 21:20
memberDrazen Dotlic31-Jul-06 21:20 
GeneralRe: Pretty redundant data type Pin
Hamed_ji31-Jul-06 23:22
memberHamed_ji31-Jul-06 23:22 
GeneralRe: Pretty redundant data type Pin
Alexey A. Popov14-Jun-06 6:25
memberAlexey A. Popov14-Jun-06 6:25 

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