Re: Question about jumps


Dragontamer wrote:
Markus Pitha wrote:
Thanks for the tipps.
As I read in AoA that shifting a byte to the left would multiply the
operand by two, I was in mood to try it out. But unfortunately it didn't
work. I have no clue why, but my following code read a number from stdin,
but doesn't display any output. What's wrong here?

segment .code

msg1 db "Enter a number: ", 0
len1 equ $-msg1

segment .bss

nmbr resb 8

segment .text
global _start

_start:
mov eax, 4 ;write
mov ebx, 1
mov ecx, msg1
mov edx, len1
int 0x80

mov eax, 3 ;read
mov ebx, 0
mov ecx, nmbr
mov edx, 8
int 0x80

mov eax, nmbr
shl eax, 1 ; nmbr * 2
mov ecx, eax ; mov it to ecx

mov eax, 4
mov ebx, 1
mov edx, 8
int 0x80

mov eax, 1 ; sys_exit
mov ebx, 0
int 0x80

You need to convert the number into a string before you can
display it.

I suggest using the C stdlib (ssprintf or itoa if its in your standard
library) or HLA's library so you can print integers directly.

If you want to do it yourself... well; just allocate the memory
in the bss section or a code section, and erm; convert it into
ascii. What else to say? You can do it easily with a recursive
function. Modulo (% in C and Java IIRC) is combined with the
div operator. When you do a divide in Assembly... bah; just
read the docs/AoA whatever.

--Dragontamer

And don't forget to do atoi (or your own homebuilt atoi) to
convert the string into an integer.

You can't just operate on strings. You have to convert into
integers before you can add, subtract, etc. etc.

--Dragontamer

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