Calculator in Assembly Language - Linux x86 & NASM

[nicoobe]

Hello,
My name is Nicholas and I am making a calculator in assembly language to be executed on an x86 processor.

Basically, my calculator asks the user to enter two numbers and then to indicate which operation (addition, subtraction, multiplication and division) want to do with them.

My calculator adds, subtracts and multiplies correctly but is unable to divide. In making a division, I always get 1 as the result.

Then I leave my application code complete:


section .data

; Messages

msg1 db 10,'-Calculator-',10,0
lmsg1 equ $ - msg1

msg2 db 10,'Number 1: ',0
lmsg2 equ $ - msg2

msg3 db 'Number 2: ',0
lmsg3 equ $ - msg3

msg4 db 10,'1. Add',10,0
lmsg4 equ $ - msg4

msg5 db '2. Subtract',10,0
lmsg5 equ $ - msg5

msg6 db '3. Multiply',10,0
lmsg6 equ $ - msg6

msg7 db '4. Divide',10,0
lmsg7 equ $ - msg7

msg8 db 'Operation: ',0
lmsg8 equ $ - msg8

msg9 db 10,'Result: ',0
lmsg9 equ $ - msg9

msg10 db 10,'Invalid Option',10,0
lmsg10 equ $ - msg10

nlinea db 10,10,0
lnlinea equ $ - nlinea

section .bss

; Spaces reserved for storing the values ​​provided by the user.

opc resb 2
num1 resb 2
num2 resb 2
result resb 2

section .text

global _start

_start:

; Print on screen the message 1
mov eax, 4
mov ebx, 1
mov ecx, msg1
mov edx, lmsg1
int 80h

; Print on screen the message 2
mov eax, 4
mov ebx, 1
mov ecx, msg2
mov edx, lmsg2
int 80h

; We get num1 value.
mov eax, 3
mov ebx, 0
mov ecx, num1
mov edx, 2
int 80h

; Print on screen the message 3
mov eax, 4
mov ebx, 1
mov ecx, msg3
mov edx, lmsg3
int 80h

; We get num2 value.
mov eax, 3
mov ebx, 0
mov ecx, num2
mov edx, 2
int 80h

; Print on screen the message 4
mov eax, 4
mov ebx, 1
mov ecx, msg4
mov edx, lmsg4
int 80h

; Print on screen the message 5
mov eax, 4
mov ebx, 1
mov ecx, msg5
mov edx, lmsg5
int 80h

; Print on screen the message 6
mov eax, 4
mov ebx, 1
mov ecx, msg6
mov edx, lmsg6
int 80h

; Print on screen the message 7
mov eax, 4
mov ebx, 1
mov ecx, msg7
mov edx, lmsg7
int 80h

; Print on screen the message 8
mov eax, 4
mov ebx, 1
mov ecx, msg8
mov edx, lmsg8
int 80h

; We get the option selected.
mov ebx,0
mov ecx,opc
mov edx,2
mov eax,3
int 80h

mov ah, [opc] ; Move the selected option to the registry ah
sub ah, '0' ; Convert from ascii to decimal

; We compare the value entered by the user to know what operation to perform.

cmp ah, 1
je add
cmp ah, 2
je subtract
cmp ah, 3
je multiply
cmp ah, 4
je divide

; If the value entered by the user does not meet any of the above
; conditions then we show an error message and we close the program.
mov eax, 4
mov ebx, 1
mov ecx, msg10
mov edx, lmsg10
int 80h

jmp exit

add:
; We keep the numbers in the registers eax and ebx
mov eax, [num1]
mov ebx, [num2]

; Convert from ascii to decimal
sub eax, '0'
sub ebx, '0'

; Add
add eax, ebx

; Conversion from decimal to ascii
add eax, '0'

; We move the result
mov [result], eax

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 1
int 80h

; We end the program
jmp exit

subtract:
; We keep the numbers in the registers eax and ebx
mov eax, [num1]
mov ebx, [num2]

; Convert from ascii to decimal
sub eax, '0'
sub ebx, '0'

; Subtract
sub eax, ebx

; Conversion from decimal to ascii
add eax, '0'

; We move the result
mov [result], eax

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 1
int 80h

; We end the program
jmp exit

multiply:

; We store the numbers in registers ax and bx
mov ax, [num1]
mov bx, [num2]

; Convert from ascii to decimal
sub ax, '0'
sub bx, '0'

; Multiply. AL = AX x BX
mul bx

; Conversion from decimal to ascii
add al, '0'

; We move the result
mov [result], al

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 1
int 80h

; We end the program
jmp exit

divide:
; IN THIS LABEL IS THE ERROR!

; We store the numbers in registers ax and bx
mov dx, 0
mov ax, [num1]
mov bx, [num2]

; Convert from ascii to decimall
sub ax, '0'
sub bx, '0'
; Division. AX = DX:AX / BX
div bx

; Conversion from decimal to ascii
add ax, '0'
; We move the result
mov [result], ax

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
; ALWAYS PRINTS 1
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 1
int 80h

; We end the program
jmp exit

exit:
; Print on screen two new lines
mov eax, 4
mov ebx, 1
mov ecx, nlinea
mov edx, lnlinea
int 80h
; End the program
mov eax, 1
mov ebx, 0
int 80h
The error must be found inside the tag "divide".

I hope that someone on the forum with more experience can help me with this. http://forum.nasm.us/Smileys/default/smiley.gif
Thanks you

[alegomaster]

I might be able to help you though it might take time. I didn't work with x86 assembly for a while (I am mostly doing risc assembly right now), but I might find the issue.

Edit: I need KDE!!!! I decided to install kubuntu onto virtual, so I am waiting for the download to finish and once it is done, I will start testing your code

Edit: what assembler are you using

[alegomaster]

Your code seems to be great so I am not sure what is wrong with it. You seemed to follow proper conventions when multiplying so I am unable to figure it out (I use GAS so I am not familiar with NASM). I will try to forward this to some people who have more experience with x86 assembly so that they can help you.

[alegomaster]

So after going on IRC and consulting with Jester01 who decided to make me figure it out, I finally got the answer. Here it is:


divide:
; IN THIS LABEL IS THE ERROR!

; We store the numbers in registers ax and bx
mov dx, 0
mov ax, [num1]
mov bx, [num2]

sub ax, 0xa00 ;New line HERE
sub bx, 0xa00

; Convert from ascii to decimall
sub ax, '0'
sub bx, '0'
; Division. AX = DX:AX / BX
div bx

; Conversion from decimal to ascii
add ax, '0'
; We move the result
mov [result], ax

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
; ALWAYS PRINTS 1
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 1
int 80h

; We end the program
jmp exit


The issue was that the system calls to record the text was also picking up the newline, so if you subtract 0xa00 from ax, then your problem is solved. Please mark the thread solved if you are finished or you can ask another question.

[nicoobe]

Thank you very much. My calculator finally works.

Here is my final code:



section .data

; Messages

msg1 db 10,'-Calculator-',10,0
lmsg1 equ $ - msg1

msg2 db 10,'Number 1: ',0
lmsg2 equ $ - msg2

msg3 db 'Number 2: ',0
lmsg3 equ $ - msg3

msg4 db 10,'1. Add',10,0
lmsg4 equ $ - msg4

msg5 db '2. Subtract',10,0
lmsg5 equ $ - msg5

msg6 db '3. Multiply',10,0
lmsg6 equ $ - msg6

msg7 db '4. Divide',10,0
lmsg7 equ $ - msg7

msg8 db 'Operation: ',0
lmsg8 equ $ - msg8

msg9 db 10,'Result: ',0
lmsg9 equ $ - msg9

msg10 db 10,'Invalid Option',10,0
lmsg10 equ $ - msg10

nlinea db 10,10,0
lnlinea equ $ - nlinea

section .bss

; Spaces reserved for storing the values ​​provided by the user.

opc: resb 2
num1: resb 2
num2: resb 2
result: resb 2

section .text

global _start

_start:

; Print on screen the message 1
mov eax, 4
mov ebx, 1
mov ecx, msg1
mov edx, lmsg1
int 80h

; Print on screen the message 2
mov eax, 4
mov ebx, 1
mov ecx, msg2
mov edx, lmsg2
int 80h

; We get num1 value.
mov eax, 3
mov ebx, 0
mov ecx, num1
mov edx, 2
int 80h

; Print on screen the message 3
mov eax, 4
mov ebx, 1
mov ecx, msg3
mov edx, lmsg3
int 80h

; We get num2 value.
mov eax, 3
mov ebx, 0
mov ecx, num2
mov edx, 2
int 80h

; Print on screen the message 4
mov eax, 4
mov ebx, 1
mov ecx, msg4
mov edx, lmsg4
int 80h

; Print on screen the message 5
mov eax, 4
mov ebx, 1
mov ecx, msg5
mov edx, lmsg5
int 80h

; Print on screen the message 6
mov eax, 4
mov ebx, 1
mov ecx, msg6
mov edx, lmsg6
int 80h

; Print on screen the message 7
mov eax, 4
mov ebx, 1
mov ecx, msg7
mov edx, lmsg7
int 80h

; Print on screen the message 8
mov eax, 4
mov ebx, 1
mov ecx, msg8
mov edx, lmsg8
int 80h

; We get the option selected.
mov ebx,0
mov ecx,opc
mov edx,2
mov eax,3
int 80h

mov ah, [opc] ; Move the selected option to the registry ah
sub ah, '0' ; Convert from ascii to decimal

; We compare the value entered by the user to know what operation to perform.

cmp ah, 1
je add
cmp ah, 2
je subtract
cmp ah, 3
je multiply
cmp ah, 4
je divide

; If the value entered by the user does not meet any of the above
; conditions then we show an error message and we close the program.
mov eax, 4
mov ebx, 1
mov ecx, msg10
mov edx, lmsg10
int 80h

jmp exit

add:
; We keep the numbers in the registers al and bl
mov al, [num1]
mov bl, [num2]

; Convert from ascii to decimal
sub al, '0'
sub bl, '0'

; Add
add al, bl

; Conversion from decimal to ascii
add al, '0'

; We move the result
mov [result], al

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 2
int 80h

; We end the program
jmp exit

subtract:
; We keep the numbers in the registers al and bl
mov al, [num1]
mov bl, [num2]

; Convert from ascii to decimal
sub al, '0'
sub bl, '0'

; Subtract
sub al, bl

; Conversion from decimal to ascii
add al, '0'

; We move the result
mov [result], al

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 1
int 80h

; We end the program
jmp exit

multiply:

; We store the numbers in registers al and bl
mov al, [num1]
mov bl, [num2]

; Convert from ascii to decimal
sub al, '0'
sub bl, '0'

; Multiply. AX = AL x BL
mul bl

; Conversion from decimal to ascii
add ax, '0'

; We move the result
mov [result], ax

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 1
int 80h

; We end the program
jmp exit

divide:

; We store the numbers in registers ax and bx
mov al, [num1]
mov bl, [num2]

mov dx, 0
mov ah, 0

; Convert from ascii to decimall
sub al, '0'
sub bl, '0'

; Division. AL = AX / BX
div bl

; Conversion from decimal to ascii
add ax, '0'
; We move the result
mov [result], ax

; Print on screen the message 9
mov eax, 4
mov ebx, 1
mov ecx, msg9
mov edx, lmsg9
int 80h

; Print on screen the result
mov eax, 4
mov ebx, 1
mov ecx, result
mov edx, 1
int 80h

; We end the program
jmp exit

exit:
; Print on screen two new lines
mov eax, 4
mov ebx, 1
mov ecx, nlinea
mov edx, lnlinea
int 80h
; End the program
mov eax, 1
mov ebx, 0
int 80h