1. CET 3510 – Lecture 11
Bit Manipulation in a High-Level Programming Language
Dr. José M. Reyes Álamo

2. Bitwise Operations
A logical operation that is performed between bit of the operand(s) in their corresponding position
Bitwise AND
Bitwise OR
Bitwise NOT
Bitwise XOR

3. Bitwise Operations Recipe: HLA Code Example: mov( eax, ecx );
Move the first operand into an appropriate register
Perform the corresponding operation proving the first and second operand
HLA Code Example:
mov( eax, ecx );
and( ebx, ecx );
or( ebx, ecx );
xor( ebx, ecx );
mov( ebx, ecx );
not( ecx ); //BE CAREFUL

4. Bitwise Operations in C/C++
Result is the same, syntax is different
Bitwise AND operator: &
Bitwise OR operator: |
Bitwise NOT operator: ~
Bitwise XOR operator: ^
Be careful:
Do not confuse these with the logical comparison operators: &&, ||, !

5. Bitwise Operations in C/C++
Code Example:
void logicalOperations(){
int x, y, z;
x = 5;
y = 2;
z = x & y;
cout << "x & y = " << z << endl;
z = x | y;
cout << "x | y = " << z << endl;
z = x ^ y;
cout << "x ^ y = " << z << endl;
z = ~x;
cout << "~x = " << z << endl;
system("PAUSE"); }

6. Shifting Left in HLA Shift left move each bit n positions to the left
Lower order bits becomes a 0
Higher order bit become a carry out
HLA code:
shl( count, dest ) | count = positions to shift; dest = register or variable
Shifting n places to the left one position is equivalent to multiplying by the base (radix) n times (radix)

7. Shifting Right in HLA
Shift right move each bit n positions to the right
Higher order bits becomes a 0
Lower order bit become a carry out
HLA code:
shr( count, dest ) | count = positions to shift; dest = register or variable
sar( count, dest ) | count = positions to shift; dest = register or variable. Used for arithmetic shifting.
Shifting n places to the right one position is equivalent to dividing by the base (radix) n times

8. Shifting in C/C++ The bitwise shifting operators are
Right shift (>>)
Left shift (<<)
Be careful with the compiler as shifting (especially shifting right) might return unexpected results

9. Shifting in C++ Code Example: void shiftingOperations(){ }
int x, y, z;
x = 2;
x = x << 5;
cout << "x shifted left = " << x << endl;
x = x >> 1;
cout << "x shifted right = " << x << endl; }

10. Bit Manipulation Example HLA
HLA Code:
stdout.put( “Enter the current month, day, and year: “ );
stdin.get( month, day, year );
mov( 0, ax );
mov( ax, packedDate ); //Just in case there is an error.
mov( month, al );
shl( 5, ax );
or( day, al );
shl( 7, ax );
or( year, al );
mov( ax, packedDate );
stdout.put( “Packed data = $”, packedDate, nl );

11. Bit Manipulation Example C++
void packedDate(){
int month, day, year, packedDate;
cout << "Enter the current month, day, and year: " << endl;
cin >> month >> day >> year;
packedDate = 0;
packedDate = packedDate | month;
packedDate = packedDate << 5;
packedDate = packedDate | day;
packedDate = packedDate << 7;
packedDate = packedDate | year;
cout << "Packed date is " << hex << packedDate << endl; }