1. Bit Manipulations
CS212

2. Bit Level Manipulators
And (&)
bitwise based on type
Or ( | )
Xor ( ^ )
Compelment ( ~ )
Shift right ( >> )
no carry, in or out; based on type
shift left ( << )

3. Bases other than 10 Binary ; base 2 ; ( 0,1)
char myint = 0b ; // 1510
Octal ; base 8 ; (0,1,2,3,4,5,6,7)
char myint2 = 0o017; // 1510
Hexadecimal ; base 16 ; (0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f)
char myint3 = 0x0f ; // 1510

4. Shifting Logical shifts – shift in a 0 as pad character
Arithmetic shifts – preserve the sign bit for right shift, act like a logical
shift for left shift
Rotate left – lsb becomes the msb
Rotate right – msb becomes lsb
In C and C++ : shifting an unsigned int acts as a logical shift
shifting a signed int acts as an arithmetic shift
rotates are not part of the language and must be done
via a user provided function

5. Shifting
unsigned char a; a = 0b << 2 ; // produces 0b
unsigned char b; b = 0xaa >> 1; // b = 0x55
//turn on bit 5
mask = ( 1 << 5 );

6. And & 1 Used for masking or extracting bits in a variable or1
Used for masking or extracting bits in a variable or
testing the status of a bit or a field in a variable
Also for turning bits off
// check to see if bit 3 in int1 is set to 1
char int1 = 0xaa; char mask3 = 0b ;
if ( int1 & mask3) printf(“bit 3 on”);
else printf(“bit3 off);
// turn bits 0 and 1 off in int4
char int4 = 0b ; char mask01 =0b ;
int4 &=mask01 ; //result is int4 = 0b ;
//clear a bit
unsigned char b &= ~(1 << n);

7. Or | 1 Usually used for turning bits on // turn on bit 31
Usually used for turning bits on
// turn on bit 3
char register = 0xaa; char bit3 = 0b ;
register |= bit3; //register is now 0b ;
// turn on bit n in a
unsigned char a |= (1 << n);

8. Xor ^ 1
Called a half add or an add with no carry; can be used to flip bits
// flip bit n in word
unsigned char word ^= (1 << n);
//set word to all zeros , xor it with itself
word ^= word;
//swap the values in a and b
(((a) ^= (b)), ((b) ^= (a)), ((a) ^= (b)))

9. Complement ~ 1 Used to flip all of the bits in a variable1
Used to flip all of the bits in a variable
unsigned char int1 = 0xaa;
int1 = ~int1 // produces int1 = 0x55;