1. The document describes various bitwise operations including AND, OR, XOR, NOT, TEST, and CMP and how they affect flags and values. 2. It provides examples of using each operation to clear/set bits, convert between binary and ASCII, check register parity, and compare values. 3. In-class problems are presented and answered involving manipulating register bits through single instructions.

1. Boolean and Comparison
Instructions
Operation Description
AND AND Destination, Source
OR OR Destination, Source
XOR XOR Destination, Source
NOT NOT Destination
TEST
Implied AND Destination, Source,
Only FLAGS changed
BT,BTC,BTR,
BTS 01/20/16 SHOUA IQBAL 1

2. 
 Bitwise AND (result placed in destination)
Mov al, 00001111b
And al, 00111011b al = ?
• al = 00001011b (0Bh)
Mov al, 6Dh
And al, 4Ah al = ?
• al = 48h
• AND with a 0 to clear bits
• AND with a 1 to preserve bits (bit extraction)
• Always clears the Overflow and Carry flags.
• May modify the Sign, Zero, and Parity flag
AND Instruction
01/20/16 SHOUA IQBAL 2

3.  Lowercase A (‘a’) is 61 0 1 1 0 0 0 0 1
 Uppercase A (‘A’) is 41 0 1 0 0 0 0 0 1
 Need to clear bit 5
Mov al, 61h
AND al, 11011111b ;(DFh)
;al = 41h
Application:Converting Characters
to Uppercase
01/20/16 SHOUA IQBAL 3

4. 
 Bitwise OR (result placed in destination)
Mov al, 0Fh
Or al, 61h al = ?
• al = 6Fh
Mov al, 3Dh
Or al, 74h al = ?
• al = 7Dh
 OR with 1 to set selected bits
 OR with 0 to preserve bits
 Always clears the Overflow and Carry Flags
 May modify the Sign, Zero, and Parity Flags
OR Instruction
01/20/16 SHOUA IQBAL 4

5.  Binary representation for 9 0 0 0 0 1 0 0 1
 Ascii 9 is 39h 0 0 1 1 1 0 0 1
 Need to set bits 4 and 5
Mov al, 9
OR al, 30h
;al = 00111001b (39h)
Application: Converting a Decimal
Digit (byte) to ASCII
01/20/16 SHOUA IQBAL 5

6. Application:Determining the sign of a
value by ORing register with itself
OR al, al
Zero Flag Sign Flag Value in AL is …
clear clear greater than 0
set clear equal to 0
clear set less than 0
01/20/16 SHOUA IQBAL 6

7. 
 Bitwise XOR (result stored in destination)
Mov al, 94h
XOR al, 37h al = ?
al = 10100011b
Mov al, 72h
Xor al, 0DCh al = ?
al = 10101110b
• XOR reverses itself when applied twice to the same
operand (data encryption)
• Clears the Overflow and Carry flags.
• May modify the sign, zero, and parity flags
XOR Instruction
01/20/16 SHOUA IQBAL 7

8. 
Indicates if the LOWEST BYTE of the result of a bitwise or
arithmetic operation has an even or odd number of 1 bits.
Mov al, 10110101b
XOR al, 0
; al unchanged parity flag clear (PO)
Mov al, 11001100b
XOR al, 0
; al unchanged parity flag set (PE)
Parity Flag
01/20/16 SHOUA IQBAL 8

9. 
Perform an XOR between upper-and lower bytes
Mov ax, 64C1h ;0110 0100 1100 0001
XOR ah, al
;ah = 10100101
Parity bit set (PE)
Application:How to check the
parity of 16-bit registers
01/20/16 SHOUA IQBAL 9

10. Perform an XOR between bytes
Mov eax, 56D764C1h
;0101 0110 1101 0111 0110 0100 1100 0001
XOR ah, al ;ah = 1010 0101
Shr eax, 8
XOR ah, al ;ah = 0111 0010
Shr eax, 8
XOR ah, al ;ah = 0010 0100
Parity bit set (PE)
Application: How to check the
parity of 32-bit registers
01/20/16 SHOUA IQBAL 10

11. 
 Toggles all bits in an operand
 No flags are affected
NOT Instruction
01/20/16 SHOUA IQBAL 11

12. 
 Implied AND (no registers are changed)
(flags may be modified)
• Valuable for determining if individual bits are set.
• Always clears the Overflow and Carry flags
• May modify the sign, zero, and parity flags
TEST Instruction
01/20/16 SHOUA IQBAL 12

13. 
 Implied SUB (no registers are changed)
(flags may be modified)
• May modify Overflow, Sign, Zero, Aux. Carry, and
Parity flags
CMP Instruction
01/20/16 SHOUA IQBAL 13

14. CMP Instruction Results
Zero Flag Carry Flag CMP Results
0 1
destination < source
CMP 5, 10
0 0
destination > source
CMP 105, 10
1 0
destination = source
CMP 10, 10
01/20/16 SHOUA IQBAL 14

15. CMP of Signed Integers
Flags CMP Results
SF ≠ OF destination < source
SF = OF destination > source
ZF = 1 destination = source
01/20/16 SHOUA IQBAL 15

16. 
1. Write a single instruction that clears the high 8 bits
of AX and does not change the low 8 bits.
AND AX, 00FFh
In Class Problems
01/20/16 SHOUA IQBAL 16

17. 
2. Write a single instruction that sets the high 8 bits of
AX and does not change the low 8 bits.
OR AX, FF00h
In Class Problems
01/20/16 SHOUA IQBAL 17

18. 
3. Write a single instruction that complements all the
bits in EAX (do not use the NOT instruction)
XOR EAX, FFFFFFFFh
In Class Problems
01/20/16 SHOUA IQBAL 18

19. 
4. Write instructions that set the Zero flag if the 32-bit
value in EAX is even, and clear the Zero flag if EAX
is odd.
TEST EAX, 0000 0000 0000 0000 0000 0000 0000
0001b
In Class Problems
01/20/16 SHOUA IQBAL 19