1. Ch. 7 Logic, Shift and Rotate instr.
Logic Instructions
AND, OR, XOR and NOT
TEST Instruction
Shift Instructions
Left shift – doubles a number
Right shift – halves a number
… multiply or divide by powers of 2
MUL, DIV – much slower than shift instr…
Rotate
Stack Operations
Introduction to Procedures

2. 7.1 AND, OR and XOR Instructions
AND destination, source
OR destination, source
XOR destination, source
Dest. – must be a Register or mem.
Source – const, reg., mem
Memory-to-memory operations are not allowed
Effect on flags
SF, ZF, PF reflect the result
AF is undefined
CF, OF = 0
SF – sign
ZF – zero
PF – parity
AF – auxiliary carry
OF – overflow
CF – carry

3. Use of Logic Instructions
Selectively modify the bits of destination
b AND 1 = b (b represents a bit, 0/1)
b AND 0 = 0
b OR 0 = b
b OR 1 = 1
b XOR 0 = b
b XOR 1 = ~b (complement of b)
So, AND can be used to clear specific destination bit
OR can be used to set specific destination bit
XOR can be used to complement specific destination bit

4. Examples
mask
Example 7.2: Clear the sign bit of AL while leaving the other bits unchanged.
AND AL, 7Fh
Example 7.3: Set the msb and lsb of AL while preserving the other bits.
OR AL, 81h
Example 7.4: Change the sign bit of DX
XOR DX, 8000h
= 7Fh
= 81h
See example from book

5. How to clear a register? MOV AX, 0 ; machine code 3 bytes
SUB AX, AX ; .. 2 bytes
XOR AX, AX ; .. 2 bytes
-- BUT mem2mem operations only for MOV is allowed here – so to clear a memory location, use MOV.

6. 7.1.2 NOT Instruction 1’s Complement operation NOT destination
No effect on status flags
Example 7.5: Complement the bits in AX
NOT AX

7. 7 Logic Instructions TEST Instruction Shift and Rotate Instructions
AND, OR, XOR and NOT
TEST Instruction
Shift and Rotate Instructions
Stack Operations
Introduction to Procedures

8. 7.2 TEST Instruction
TEST performs AND of the destination with source – but no change of the dest. contents
TEST destination, source
Effects on flags
SF, ZF, PF reflect the result
AF is undefined
CF, OF = 0
TEST vs. CMP
CMP is subtraction operation

9. JZ – jump if equal to zero
TEST Example
Jump to label BELOW if AL contains an even number
TESET AL, 1 ; is AL even?
JZ BELOW ; yes, go to BELOW
JZ – jump if equal to zero
use to examine individual bits in an operand.
mask contains 1’s in the bits positions to be tested & 0’s elsewhere
Even numbers have a 0 in bit#0.
So, mask = b = 1

10. Agenda Logic Instructions TEST Instruction
AND, OR, XOR and NOT
TEST Instruction
Shift and Rotate Instructions
Stack Operations
Introduction to Procedures

11. 7.2 Shift and Rotate Instructions
Two types of shift and rotate instructions
Logical Shift / Rotate
Arithmetic Shift/Rotate
Both logical and arithmetic left shift are identical
But right shifts are different

12. opcode dest, 1 ; 1 bit change opcode dest, CL ; N bits change
; CL contians N
Dest  reg., mem
SHL  Multiplication by left shift by multiplies of 2
SAL  for numeric multiplication

13. Shift and Rotate Instructions
SHL DH, 3 ; DH =
DH =
C = 1
SHR DH, 3 ; DH =
DH =
C = 1
SAL DH, 2 ; DH =
DH =
C = 1
SAR DH, 2 ; DH =
DH =
C = 1

14. Rotate Instructions ROL – rotate left ROR – r right RCL – r carry left
RCR – r c right
Let
DH = 8Ah =
CF = 1
After first RCR
DH = CF = 0
After second RCR
DH = CF = 1

15. Agenda Logic Instructions TEST Instruction
AND, OR, XOR and NOT
TEST Instruction
Shift and Rotate Instructions
Stack Operations

16. Stack vs. Queue Stack Queue LIFO : Last In First Out
FIFO : First In First Out
Queue
Stack

17. PUSH vs. POP in Stack

18. PUSH Instructions

19. POP Instructions

20. References Some materials are from Dr. Sazzad, NSU
Ch 7, Assembly Language Programming – by Charls Marut
Ch 4, Intel Microprocessors – by Brey