Lab 7
Lab 7 : Programming based on Bit Manipulation
Objective
To familiar with bit manipulation methods.
Prelab
Read Instructions related to Logical and shift the operands.
Bit Manipulation instructions
Instructions | Operands | Description |
AND | • REG, memory
• memory, REG
• REG, REG
• memory,immediate
• REG, immediate | Logical AND between all bits of two operands. Result is stored in operand1.
These rules apply:
1 AND 1 = 1; 1 AND 0 = 0
0 AND 1 = 0; 0 AND 0 = 0 |
OR | • REG, memory
• memory, REG
• REG, REG
• memory, immediate
• REG, immediate | Logical OR between all bits of two operands. Result is stored in first operand.
These rules apply:
1 OR 1 = 1; 1 OR 0 = 1
0 OR 1 = 1; 0 OR 0 = 0 |
XOR | • REG, memory
• memory, REG
• REG, REG
• memory, immediate
• REG, immediate | Logical XOR (Exclusive OR) between all bits of two operands. Result is stored in first operand.
These rules apply:
1 XOR 1 = 0; 1 XOR 0 = 1
0 XOR 1 = 1; 0 XOR 0 = 0 |
SHL | • memory, immediate
• REG, immediate
• memory, CL
• REG, CL | Shift Left.
Shift operand1 Left. The number of shifts is set by operand2.
Algorithm:
• Shift all bits left, the bit that goes off is set to CF.
Zero bit is inserted to the right-most position. |
SHR | • memory, immediate
• REG, immediate
• memory, CL
• REG, CL | Shift Right.
Shift operand1 Right. The number of shifts is set by operand2.
Algorithm:
• Shift all bits right, the bit that goes off is set to CF.
• Zero bit is inserted to the left-most position. |
ROL | • memory, immediate
• REG, immediate
• memory, CL
• REG, CL | Rotate Left.
Rotate operand1 left. The number of rotates is set by operand2.
Algorithm:
Shift all bits left, the bit that goes off is set to CF and the same bit is inserted to the right-most position. |
RCL | • memory, immediate
• REG, immediate
• memory, CL
• REG, CL | Rotate operand1 left through Carry Flag. The number of rotates is set by operand2.
Algorithm:
Shift all bits left, the bit that goes off is set to CF and previous value of CF is inserted to the right-most position.
Example:
STC ; set carry (CF=1).
MOV AL, 1Ch ; AL = 00011100b
RCL AL, 1 ; AL = 00111001b, CF=0.
RET
OF=0 if first operand keeps original sign. |
ROR | • memory, immediate
• REG, immediate
• memory, CL
• REG, CL | Rotate Right.
Rotate operand1 right. The number of rotates is set by operand2.
Algorithm:
Shift all bits right, the bit that goes off is set to CF and the same bit is inserted to the left-most position. |
Exercises
1) Write a program to check if given data is positive or negative.
section .data
prompt db "Enter a number: ", 0
positive_msg db "The number is positive.", 0
negative_msg db "The number is negative.", 0
zero_msg db "The number is zero.", 0
section .bss
num resb 4
section .text
global _start
_start:
; Print prompt
mov eax, 4
mov ebx, 1
mov ecx, prompt
mov edx, 18
int 0x80
; Read input
mov eax, 3
mov ebx, 0
mov ecx, num
mov edx, 4
int 0x80
; Convert ASCII to integer
mov eax, [num]
sub eax, '0'
; Check if positive, negative, or zero
cmp eax, 0
jg positive
jl negative
je zero
positive:
mov ecx, positive_msg
mov edx, 23
jmp print
negative:
mov ecx, negative_msg
mov edx, 23
jmp print
zero:
mov ecx, zero_msg
mov edx, 19
print:
mov eax, 4
mov ebx, 1
int 0x80
; Exit program
mov eax, 1
xor ebx, ebx
int 0x802) Write a program to check if given data is odd or even.
section .data
prompt db "Enter a number: ", 0
odd_msg db "The number is odd.", 0
even_msg db "The number is even.", 0
section .bss
num resb 4
section .text
global _start
_start:
; Print prompt
mov eax, 4
mov ebx, 1
mov ecx, prompt
mov edx, 18
int 0x80
; Read input
mov eax, 3
mov ebx, 0
mov ecx, num
mov edx, 4
int 0x80
; Convert ASCII to integer
mov eax, [num]
sub eax, '0'
; Check if odd or even
test al, 1
jz even
odd:
mov ecx, odd_msg
mov edx, 18
jmp print
even:
mov ecx, even_msg
mov edx, 19
print:
mov eax, 4
mov ebx, 1
int 0x80
; Exit program
mov eax, 1
xor ebx, ebx
int 0x803) Write a program to count the number of 1’s and 0’s in given data.
section .data
prompt db "Enter a number: ", 0
ones_msg db "Number of 1's: ", 0
zeros_msg db "Number of 0's: ", 0
section .bss
num resb 4
ones_count resb 1
zeros_count resb 1
section .text
global _start
_start:
; Print prompt
mov eax, 4
mov ebx, 1
mov ecx, prompt
mov edx, 18
int 0x80
; Read input
mov eax, 3
mov ebx, 0
mov ecx, num
mov edx, 4
int 0x80
; Convert ASCII to integer
mov al, [num]
sub al, '0'
; Initialize counters
mov byte [ones_count], 0
mov byte [zeros_count], 0
mov cl, 8 ; Loop counter (8 bits)
count_loop:
shr al, 1 ; Shift right to check least significant bit
jc increment_ones
inc byte [zeros_count]
jmp continue
increment_ones:
inc byte [ones_count]
continue:
dec cl
jnz count_loop
; Print results
mov eax, 4
mov ebx, 1
mov ecx, ones_msg
mov edx, 16
int 0x80
mov al, [ones_count]
add al, '0'
mov [num], al
mov eax, 4
mov ebx, 1
mov ecx, num
mov edx, 1
int 0x80
mov eax, 4
mov ebx, 1
mov ecx, zeros_msg
mov edx, 17
int 0x80
mov al, [zeros_count]
add al, '0'
mov [num], al
mov eax, 4
mov ebx, 1
mov ecx, num
mov edx, 1
int 0x80
; Exit program
mov eax, 1
xor ebx, ebx
int 0x80