Getting digit instead of Ascii in nasm assembly intel x86

Question

I'm trying to learn the basics of assembly but can't get across on how to display results stored in memory.

section .data
    num1 db 1,2,3,4,5
    num2 db 1,2,3,4,5

    output: db 'The dot product is "'
    outputLen1 : equ $-output
    output2: db '" in Hex!', 10
    output2Len : equ $-output2


section .bss
    dotProd resw 1  ; store dot product in here

section .text
        global _start

_start:
                mov eax, 0
                mov ecx, 5
                mov edi, 0
                mov esi, 0
looper:         mov ax, [edi + num1]
                mov dx, [esi + num2]
                mul dx
                add [dotProd], ax
                cmp cx, 1
                je printOutput
                inc edi
                inc esi
                dec cx
                jmp looper  ; go back to looper

printOutput: 

            mov eax,4            ; The system call for write (sys_write)
            mov ebx,1            ; File descriptor 1 - standard output
            mov ecx, output      ; 
            mov edx, outputLen1  ; 
            int 80h              ; Call the kernel

            mov eax, 4
            mov ebx, 1
            mov ecx, dotProd,
            mov edx, 1
            int 80h

            mov eax, 4
            mov ebx, 1
            mov ecx, output2,
            mov edx, output2Len
            int 80h           

            jmp done
done:
            mov eax,1            ; The system call for exit (sys_exit)
            mov ebx,0            ; Exit with return code of 0 (no error)
            int 80h

What I'm trying to do is get the dot product of the two list of numbers and display it on the screen. However, I keep getting random letters which I believe are hex representations of the real decimal value. How can I convert it to decimal? The current value display is 7, which should is the equivalent ASCII char for 55, which in this case is the dot product of both list of numbers.

If someone is going to down-vote, at least provide explanation. — Dimitri, Apr 23 '15 at 21:43

score 1 · Accepted Answer · edited May 23 '17 at 11:46

esi and edi must be increased such that it points to next element of array.(in this particular example, only one of them is sufficient).
declare mun1 andnum2 as dd, instead of db (see here). Also, you have to have method for printing number.(see this and this).

Below is a complete code which uses printf.

;file_name:test.asm
;assemble and link with:
;nasm -f elf test.asm && gcc -m32 -o test test.o
extern printf
%macro push_reg 0
push eax
push ebx
push ecx
push edx
%endmacro
%macro pop_reg 0
pop edx
pop ecx
pop ebx
pop eax
%endmacro
section .data
    num1: dd 1,2,3,4,5
    num2: dd 1,2,3,4,5
    msg: db "Dot product is %d",10,0

section .bss
    dotProd resd 1  ; store dot product in here

section .text
        global main

main:
                mov eax, 0
                mov ecx, 5
                mov edx, 0
                mov esi, 0
                mov dword[dotProd], 0h
looper:         mov eax, dword[esi + num1]
                mov edx, dword[esi + num2]
                mul edx

                add [dotProd], eax

                cmp cx, 1
                je printOutput
                add esi,4
                dec cx

                jmp looper  ; go back to looper

printOutput: 

        push_reg
        push dword[dotProd]
        push dword msg
        call printf
        add esp,8
        pop_reg

        jmp done
done:
        mov eax,1            ; The system call for exit (sys_exit)
        mov ebx,0            ; Exit with return code of 0 (no error)
        int 80h

I'll definitely have to look at the printf function; I'm not entirely sure what the workings of it is as you've shown. — Dimitri, Apr 23 '15 at 21:47

Getting digit instead of Ascii in nasm assembly intel x86

1 Answers1