Question

1.Write an assembly language program that corresponds to the following C++ program:

#include <iostream>
using namespace std;

const int amount = 20000;
int num;
int sum;

int main () {

cin >> num;
sum = numb + amount;
cout << "sum = " ,<< sum << endl;
return 0;

}

2. Test the program in the previous question twice. The first time, enter a value for num to make the sum within the allowed range for the Pep/8 computer. The second time, enter a value that is in range but that makes sum outside the range. Not that the out-of-range condition does not cause an error message, but just gives an incorrect value. Explain the value.

Answer 1

SYS_EXIT  equ 1

SYS_READ  equ 3

SYS_WRITE equ 4

STDIN     equ 0

STDOUT    equ 1

AMOUNT    equ 20000 

segment .data 

    msg1 db "Enter a digit ", 0xA,0xD 

    len1 equ $- msg1 

    msg2 db " The sum is: ", 0xA,0xD 

    len2 equ $- msg2 

segment .bss

    num resb 2 

    sum resb 1    

section       .text

    global _start    ;must be declared for using gcc

_start:    ;tell linker entry point

    mov eax, SYS_WRITE         

    mov ebx, STDOUT         

    mov ecx, msg1         

    mov edx, len1 

    int 0x80                

    mov eax, SYS_READ 

    mov ebx, STDIN  

    mov ecx, num 

    mov edx, 2

    int 0x80            

    mov eax, SYS_WRITE        

    mov ebx, STDOUT         

    mov ecx, msg2          

    mov edx, len2         

    int 0x80

    mov eax, SYS_READ  

    mov ebx, STDIN  

    mov ecx, AMOUNT 

    mov edx, 2

    int 0x80        

    mov eax, SYS_WRITE         

    mov ebx, STDOUT         

    mov ecx, msg3          

    mov edx, len3         

    int 0x80

    ; moving the first number to eax register and second number to ebx

    ; and subtracting ascii '0' to convert it into a decimal number

    mov eax, [num]

    sub eax, '0'

    mov ebx, [AMOUNT]

    sub ebx, '0'

    ; add eax and ebx

    add eax, ebx

    ; add '0' to to convert the sum from decimal to ASCII

    add eax, '0'

    ; storing the sum in memory location res

    mov [sum], eax

    ; print the sum 

    mov eax, SYS_WRITE        

    mov ebx, STDOUT

    mov ecx, sum         

    mov edx, 1        

    int 0x80

exit:    

    mov eax, SYS_EXIT   

    xor ebx, ebx 

    int 0x80