Calculate and Display Sum
This assembly code calculates the sum of three numbers and displays the result using system calls. The code takes advantage of x86 assembly language and Linux system calls for input and output operations.
source code
section .text
global _start ; Declare entry point for linker (ld)
_start:
mov eax,3 ; Number of bytes to be summed (counter)
mov ebx,0 ; EBX will store the sum
mov ecx, x ; ECX will point to the current element to be summed
top:
add ebx, [ecx] ; Add the current element to the sum
add ecx,1 ; Move pointer to next element
dec eax ; Decrement counter
jnz top ; If counter not 0, then loop again
done:
add ebx, '0' ; Convert sum to ASCII character
mov [sum], ebx ; Store result in "sum"
display:
mov edx,1 ; Message length
mov ecx, sum ; Message to write
mov ebx, 1 ; File descriptor (stdout)
mov eax, 4 ; System call number (sys_write)
int 0x80 ; Call kernel
mov eax, 1 ; System call number (sys_exit)
int 0x80 ; Call kernel
section .data
global x
x:
db 2
db 4
db 3
sum:
db 0
Code Explanation:
The provided assembly code performs the following steps:
Setup and Loop:
Registers
eax
,ebx
, andecx
are used to manage operations and data.The loop starts with the
_start
label and iterates over thex
array's elements to calculate the sum.
Sum Calculation:
Inside the loop, each element of the
x
array is added to theebx
register (used as a sum accumulator).The
add
anddec
instructions are used to perform these operations, with the loop condition checked usingjnz
(jump if not zero).
ASCII Conversion:
After the loop, the sum in the
ebx
register is converted into its ASCII character representation by adding the ASCII value of '0'.
Displaying the Result:
The
sys_write
system call (usingint 0x80
) is used to display the result on the screen.The
sys_exit
system call is used to terminate the program.
Data Storage:
The
x
array contains the input numbers.The
sum
variable stores the ASCII representation of the calculated sum.
Example:
Let's consider the values in the x
array: 2, 4, and 3.
The code will calculate the sum: 2 + 4 + 3 = 9.
The sum 9 will be converted to its ASCII character representation ('9') and displayed on the screen.
When the code is assembled and executed in a suitable x86 assembly environment, the output will be:
9
Usage:
To run the code:
Assemble the code using an x86 assembly assembler, for example:
nasm -f elf file.asm -o file.o
Link the object file to create an executable:
ld -m elf_i386 -s -o file file.o
Run the executable:
./file
Please ensure that you have an appropriate x86 assembly environment and that you're running this code on a Linux-based system to observe the expected output.
Feel free to replace "file" in the usage commands with a suitable name for your executable.
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