LinuxQuestions.org - nasm assembler; output numbers?

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nasm assembler; output numbers?

Probably a very simple question - I am just starting assembler. If I have something like:

Code:

...

mov eax,20 ;20==getpid

int 0x80

...

now eax should contain my processes' PID I believe? My question is this: how do I print this. I have been using:

Code:

...

mov eax,4 ;4==write

mov ebx,1 ;1==stdout

mov ecx,buf ;some memory address holding the string

mov edx,len ;length of string

int 0x80

...

which works fine for ascii strings. I can get the PID out of eax an into memory, but do I then have to convert the number into ascii, or is there a simpler way?

Thanks

My assembly knowledge is limited to microcontrollers and at this stage very rusty.
AFAIK you have to do the conversion yourself.

Below some pseudo-code that might help you on the way:

Code:

// first digit

buf[0]=(pid%10)+0x30;

pid/=10;

// second digit

buf[1]=(pid%10)+0x30;

pid/=10;

 .

 .

 .

The trick is to separate each digit and convert it to an ascii value. Separation is done by using the modulo-10.
Conversion is done by simply adding 30hex.
After the conversion, we divide the pid by 10 so we can use the modulo-10 on the next digit.

Please note that the above example places the digits in reverse order in the buffer.
Hope this helps you on the way.

Nice to have someone new to assembler programing

O.K. the code above you got posted is a little difficult to convert to NASM and would than be code of
(I guess) 600 lines.
And yes, you have to convert the value to ascii-numbers you can read.
In assembler you have all to do on your own in assembler there are no were lying
headers and libraries around like with c++.

Now here a procedure to convert the value of eax
from my homepage: beckware.de - INFO - software - NASM - examples
or direct: http://people.freenet.de/beckware/na...xtostdout.html
there are also other useful things.
Have also a look to the NASM forum:
http://sourceforge.net/forum/?group_id=6208

Code:

;

-------------------------------------------------

;Writes the value of eax to the standard output as decimal.

;-------------------------------------------------



stdout:

section .data



.buf                db        '0000000000',10,0



section .text

        pushad

        

        mov        ebx,.buf+9

        mov        ecx,10

        mov        edi,10

.a:

        mov        edx,0

        div        edi

        add        edx,48

        mov        [ebx],dl

        dec        ebx

        loop        .a



        mov        eax,4                        ;schreibe

        mov        ebx,1                        ;auf Terminal 

        mov        ecx,.buf

        mov        edx,11                ;11 Bytes

        int        $80



        popad

        ret

What happens here:
With div edi, eax is divided by 10 and edx holds the rest. Ascii ´0´ is decimal 48 and that is added to edx and stored into .buf back-wards. Now .buf is written to STDOUT that´s all.

Ah thank you. That works great, thanks for the explaination to, I understand how it is done now! I did try to convert Wim Sturkenboom's code to NASM, but I couldn't quite do it. The DIV operator confused me somewhat, but after reading the manual carefully and looking at your code/explaination i think i understand it now.

Thanks a lot.

Bumping there for telling you this solution still working perfectly.
Is clean and easy to understand.

Thank you.