A bit is 0 or 1 . All data in the computer is stored in the binary format as streams of 0 , 1.
Bitwise operators act on each bit of data of the operands. Thus associativity is immaterial in case of bitwise & , | , ^ , ` operators.
Following are bitwise operators:
& Bitwise and
| Bitwise or
~ Bitwise Not or Complment
^ Bitwise XOR (Exclusive or)
>> Right Shift
<< Left Shift
Assignment operators combined with bitwise operators :-
&=
|=
^=
>>=
<<=
Bitwise ‘and’ & Operator : (called anding) is a binary operator that returns 1 if both operands are 1 else returns 0 . Acts on each bit of data .
Program 1 :- Bitwise & operator
void main( )
{
char x = 100 , y = 53 , z ;
clrscr( );
z = x & y ;
printf(“z = %d” , z ); /* prints z = 36 */
}
x è 0110 0100 /* 100 */
y è 0011 0101 /* 53 */
z = x & y è 0010 0100 /* 36 */
Bitwise ‘or’ | Operator : is a binary operator that returns 1 if any one operand is 1 else returns 0 . Acts on each bit of data .
Program 2 :- Bitwise | operator
void main( )
{
char x = 100 , y = 53 , z ;
clrscr( );
z = x | y ;
printf(“z = %d” , z ); /* prints z = 117 */
}
x è 0110 0100 /* 100 */
y è 0011 0101 /* 53 */
z = x | y è 0111 0101 /* 117 */
Bitwise XOR ^ Operator : (mutually excusive or) is a binary operator that returns 1 if any one operand is 1 and one operand is 0 .If both are 1 or both are zero , ^ operator returns 0 . Acts on each bit of data .
Program 3:-
void main()
{
char x = 100 , y = 53 , z ;
clrscr( );
z = x ^ y ;
printf(“z = %d” , z ); /* prints z = 81 */
}
x è 0110 0100 /* 100 */
y è 0011 0101 /* 53 */
z = x ^ y è 0101 0001 /* 81 */
Bitwise Complement or not ~ Operator : is a unary operator that toggles bits if 1 then it becomes 0 and vice versa. Acts on each bit of data .
Program 3:-
void main()
{
char x = 100 , z ;
clrscr( );
z = ~y ;
printf(“z = %d” , z ); /* prints z = */
}
x è 0110 0100 /* 100 */
z = ~x è 1001 1011 /* - 101 */
How is 1001 1011 interpreted ?
Since the left most bit or the most significant bit (msb) is on , the data is negative. We must take a 2’s complement to find the numerical value
Z è 1001 1011
1’s complement è 0110 0100
Add 1 1
2’s Complement è 0110 0101 /* -101 */
The bits get shifted to left or right positions
A shift is not a rotation .This means the bits shifted out on the right side will not come and fill up from the left side.
Bit representation of x :
x >> 2
For e.g
If x = 0110 0110 then x << style=""> 1001 1000
If x = 0110 0110 then x << style=""> 0011 0000
If x = 0110 0110 then x >> 2 will give 0010 0110
If x = 0110 0110 then x >> 3 will give 0010 0110
Right Shift of a negative number :-
In case of a negative number , the left most bit is set to 1 . A right shift results in 1’s fill in from the left side to fill up instead of 0’s
If x = 1110 0110 then x >> 2 will give 1111 1001
If x = 1110 0110 then x >> 3 will give 1111 1100
Assignment operators with Bitwise operators :-
&= An expression like x &= y is equivalent to x = x & y
|= An expression like x |= y is equivalent to x = x | y
^= An expression like x ^= y is equivalent to x = x ^ y
>>= An expression like x >>= y is equivalent to x = x >> y
<<= An expression like x <<= y is equivalent to x = x <<>
Application of bitwise operators :-
While software programs are byte oriented, hardwares are bit oriented.As bitwise operators act on each bit of data , One byte of information can be treated as 8 pieces of informations .Each information can be checked and manipulated.
For e.g video memory stores 1 byte for each character attributes .This 1 byte represents 8 bits of information of screen attributes of fore color, back color as shown above.
File Encryption program using bitwise complement ~ operator:
Encryption means changing the contents of a file into an illegible format for protection .Pass the file name to a command called encrypt as a command parameter
For e.g:
C:> encrypt file1
This call changes the contents of file1 into an illegible format.
/*
File encryption
command line encryption
Bitwise complement used for encryption
*/
# include
# include
main(int argc , char *argv[])
{
char ch ;FILE *fp , *ft ;
if(argc != 2)
{
printf("Error in no. of arguments");
printf("\nEncryption Failue");
exit(1);
}
if(!(fp = fopen(argv[1] , "r")) )
{
printf("Error opening file to be encrypted");
printf("\nEncryption Failue");
exit(1);
}
if(!(ft = fopen("temp" , "w")) )
{
printf("Error creating encryption file ");
printf("\nEncryption Failue");
exit(1);
}
while(!feof(fp) )
{
ch = fgetc(fp);
fputc(~ch , ft);
}
remove(argv[1]);
rename("temp" , argv[1]);
printf("\nFile Successfully encrypted");
return 0 ;
}
File Decryption program :
Decryption means restoring the contents of an encrypted file Pass the file name to a command called decrypt as a command parameter
For e.g:
C:> decrypt file1
This call recovers the file encrypted by the above encryption call
/*
File decryption
File name passed as a command line argument
Bitwise complement used for decryption
*/
# include
# include
main(int argc , char *argv[])
{
char ch ;FILE *fp , *ft ;
if(argc != 2)
{
printf("Error in no. of arguments");
printf("\nDecryption Failue");
exit(1);
}
if(!(fp = fopen(argv[1] , "r")) )
{
printf("Error in file Decryption Recovery”);
printf("\nDecryption Failue");
exit(1);
}
if(!(ft = fopen("temp" , "w")) )
{
printf("Error while decrypting ");
printf("\nDecryption Failure");
exit(1);
}
while(!feof(fp) )
{
ch = fgetc(fp);
fputc(~ch , ft);
}
remove(argv[1]);
rename("temp" , argv[1]);
printf("\nFile Successfully decrypted");
return 0 ;
}
No comments:
Post a Comment