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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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A list of licenses authors might use can be found here

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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 3:00 
Generalslow performance PinmemberZronZ7-Jan-07 22:08 
GeneralRe: slow performance [modified] Pinmemberyianfang28-Aug-07 15:51 
NewsThis guy saved my job!!!!! PinmemberPeace2u20-Jun-06 20:44 
GeneralRe: This guy saved my job!!!!! PinmemberHamed_ji31-Jul-06 12:24 
GeneralPretty redundant data type PinmemberAlexey A. Popov13-Jun-06 0:47 
GeneralRe: Pretty redundant data type PinmemberHamed_ji13-Jun-06 5:18 
GeneralRe: Pretty redundant data type Pinmemberreflex@codeproject13-Jun-06 6:10 
GeneralRe: Pretty redundant data type PinmemberHamed_ji13-Jun-06 7:51 
GeneralRe: Pretty redundant data type PinmemberAlexey A. Popov13-Jun-06 7:33 
GeneralRe: Pretty redundant data type PinmemberHamed_ji13-Jun-06 8:40 
I don't think it's good to say a class(Any class) can provide every thing, every one need. BitArray class don't provide shifting, convert BitArray to Byte array or other kind of array. and don't provide SubArray from specific bit with specific length.
 
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
 
one of the main usage of bitArray class can be encryption/decryption in there bit order is SO IMPORTANT because in encryption/decryption always you need specific bit numbers, changing them, shifting, take apart Bits to two arrays three arrays even more. so you need the functions to what i've mentioned. how you believe it covert all needs ? the main problem is indexer of BitArray class because as i said in storing inverse it. and when you use pointer you get wrong bit.
 
the data come to BitArray class and go. in must of algorithms it don't need to access 100GB of BITS. when you want encrypt/decrypt you only use blocks of your data not all of it(for example in DES encryption algorithm you only work on 64bits of data). as you know we don't save BitArray class as it is. in none encryption/decryption algorithm there no need to all data either. so the memory is not as important as speed.
 
and i think converting in ArrayList take less time than calculating bit numbers and their values
 
Hamed JI
AnswerRe: Pretty redundant data type PinmemberDrazen Dotlic14-Jun-06 0:34 
AnswerRe: Pretty redundant data type PinmemberHamed_ji31-Jul-06 12:22 
AnswerRe: Pretty redundant data type PinmemberDrazen Dotlic31-Jul-06 21:20 
GeneralRe: Pretty redundant data type PinmemberHamed_ji31-Jul-06 23:22 
GeneralRe: Pretty redundant data type PinmemberAlexey A. Popov14-Jun-06 6:25 

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