1. CS-401 Computer Architecture & Assembly Language Programming
Lecture-12
Bits Manipulation

2. Lets revise the last lecture

3. Lets revise the last lecture.

4. Extended Shift num1: dd 40000 sh1 word [num1+2],1 rc1 word [num1],1
Shift Right
num1: dd 40000
sh1 word [num1+2],1
rc1 word [num1],1
num1 + 2
num1

5. Types of Logical Operations

6. Bitwise Logical Operators
and
and performs the logical bitwise ‘and’ of two operands (byte or word) and return the result to the destination operand.
A bit in the result is set if both corresponding bits of the original operands are set. Otherwise the result bit is cleared.
Flags affected: C O P S Z A
and ax, bx
and byte [num], 5
Truth table X Y
X and Y 1

7. Bitwise Logical Operators
or performs the logical bitwise ‘Inclusive or’ of two operands (byte or word) and return the result to the destination operand.
A bit in the result is set if either or both corresponding bits of the original operands are set. Otherwise the result bit is cleared.
Flags affected: C O P S Z A
or ax, bx
or byte [num], 5
Truth table X Y
X or Y 1

8. Bitwise Logical Operators
xor
xor performs the logical bitwise ‘Exclusive or’ of two operands (byte or word) and return the result to the destination operand.
A bit in the result is set if the corresponding bits of the original operands contains opposite values. Otherwise the result bit is cleared.
Flags affected: C O P S Z A
xor ax, bx
xor byte [num], 5
Truth table X Y
X xor Y 1

9. Bitwise Logical Operators
not
not inverts the bits (forms the 1’s complement) of the word or byte operand.
Flags affected: NONE
not ax
not cl
not byte [num]
Truth table X
not X 1

10. Masking Bits and and al, 0x0F 1 0 1 0 1 0 1 0 AL = 0xAA
mask = 0x0F
AL = 0x0A

11. Masking Bits or or al, 0xF0 1 0 1 0 1 0 1 0 AL = 0xAA 1 1 1 1 0 0 0 0
mask = 0xF0
AL = 0x0A

12. Masking Bits xor xor al, 0xF0 1 0 1 0 1 0 1 0 AL = 0xAA
mask = 0xF0