- Write a program that
- prompts the user for an integer postfix arithmetic expression, which may include operators, ‘+’, ‘-’ and ‘=’, and one-digit operands, such as “62-7+=”
- calculates the postfix expression by using the runtime stack, and
- displays the result.
For example, “35-86+-= -16” and “51-5+3-37+-= -4.”
No error checking is required. (40%)
Ans>
INCLUDE Irvine32.inc
.code
main PROC
L1: call ReadChar
call WriteChar
cmp al, '+'
jne L2
pop ebx
pop eax
add eax, ebx
push eax
jmp L1
L2: cmp al, '-'
jne L3
pop ebx
pop eax
sub eax, ebx
push eax
jmp L1
L3: cmp al, '='
jne L4
pop eax
call WriteInt
jmp L5
L4: sub al, '0'
movsx eax, al
push eax
jmp L1
L5: call Crlf
call Crlf
exit
main ENDP
END main
- In the following instruction sequence, show the changed value of
AL where indicated, in binary: (16%)
mov al, 10011001b
and al, 0C5h ; AL = 81h = 10000001b
mov al, 92h
not al ; AL = 6Dh = 01101101b
mov al, 10010010b
or al, 6Dh ; AL = 0FFh = 11111111b
mov al, 0C7h
xor al, 5Eh ; AL = 99h = 10011001b
- In the following instruction sequence, show the values of the
Carry, Zero, and Sign flags where indicated: (18%)
mov al, 01101010b
test al, 0B5h ; CF = 0 ZF = 0 SF = 0
mov al, 80h
cmp al, 1 ; CF = 0 ZF = 0 SF = 0
mov al, 0FFh
cmp al, -1 ; CF = 0 ZF = 1 SF = 0
- Write a single instruction that reverses the high 4 bits of
AL and does not change the low 4 bits. (12%)
Ans>
xor al, 0F0h
- Write instructions that clear the bits 1, 3, 5, and 7 in
AL.
If the destination operand is greater or equal to 1, jump to L3.
Otherwise, jump to label L4. (14%)
Ans>
and al, 55h
cmp al, 1
jge L3
jmp L4