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Problem with number printing function
Posted: Mon Mar 11, 2013 3:15 pm
by makuc9
so I have written a function to write a number higher than 9 to the screen. But as soon as I push a value to the stack, I can't print anything using BIOS interrupt until the stack is empty again. Is there a way to go around this?
Here is the code:
Code: Select all
print_int: ; Breaks number in ax register to print it
mov cx, 10
mov bx, 0
break_num_to_pics:
cmp ax, 0
je print_all_pics
div cx
push dx
inc bx
jmp break_num_to_pics
print_all_pics:
cmp bx, 0 ; tests if bx is already null
je f_end
pop ax
add ax, 30h
call print_char
dec bx
jmp print_all_pics
print_char: ; Function to print single character to screen
mov ah, 0eh ; Prepare registers to print the character
int 10h ; Call BIOS interrupt
ret
f_end: ; Return back upon function completion
ret
If I disable the loop (remove "push" and "pop" functions, everything concerned with bx stack size tracking and the final print_all_pics loop, I can successfully print the first number (example. I try printing 9573, I can successfully print 9) or everything in reverse order (well, this would also do the trick, but I'd still like to know what I am doing wrong, for learning purposes).
Any help appreciated.
Sincerely.
Re: Problem with number printing function
Posted: Mon Mar 11, 2013 4:24 pm
by TightCoderEx
Before each division, clear contents of DX.
Code: Select all
break_num_to_pics:
cmp ax, 0
je print_all_pics
XOR DX, DX
idiv cx
push dx
inc bx
jmp break_num_to_pics
Re: Problem with number printing function
Posted: Tue Mar 12, 2013 1:32 am
by egos
I see that 0 isn't number for you.
And, makuc9, it's asm so you should optimize your code by hand. For example:
Code: Select all
mov bx,10
xor cx,cx
@@:
xor dx,dx
div bx
inc cx
push dx
and ax,ax
jnz short @b
@@:
pop ax
add al,"0"
call putchar
loop @b
ret
Re: Problem with number printing function
Posted: Tue Mar 12, 2013 3:47 am
by makuc9
egos wrote:I see that 0 isn't number for you.
And, makuc9, it's asm so you should optimize your code by hand. For example:
Code: Select all
mov bx,10
xor cx,cx
@@:
xor dx,dx
div bx
inc cx
push dx
and ax,ax
jnz short @b
@@:
pop ax
add al,"0"
call putchar
loop @b
ret
One question, where is the @b? (i think you've made a typo...) Thanks for all your help. Will test it all out soon.
Re: Problem with number printing function
Posted: Tue Mar 12, 2013 4:51 am
by Combuster
It's a label shorthand, meaning the preceding label (jmp @b/@f = jump to the first @ found backward/forward in the code), but it's not present in all assemblers - actually I can guess the exact assembler he wrote it for.
Re: Problem with number printing function
Posted: Thu Mar 14, 2013 8:27 am
by makuc9
Thanks for explaination, Combuster.
This function is needed for temporary preview (in case i will need it) of calculated values, and I am not sure yet I will keep it in completed bootloader, so I did not really paid much attention to optimazing it ... But thanks anyway. I will be testing it out and studying its structure.
Re: Problem with number printing function
Posted: Wed Apr 03, 2013 2:22 pm
by makuc9
Hello, for my late reply, but I've been working on some other parts of my bootloader and I have run out of 512b limit (I did managed to get rid of some useless data to get within the limit again) but than I remembered the updated integer printing function from egos. I copied it and compiled it. NASM however, complains about '@@' symbol being repeated. For which compiler did you made this function for? (I did solved the problem by renaiming them to '@a' and '@b', but I'd still want to know if there is something similar for NASM, since it would be useful).
Re: Problem with number printing function
Posted: Wed Apr 03, 2013 2:51 pm
by Combuster
NASM ... compiler
assemblers aren't compilers
NASM and their kin have the local label shorthand: start a label or reference to one with a . and the assembler will prepend the last label without a leading period to create the complete name. Just having @f and @b yields the problem that you still need to explicitly name labels globally unique whenever you nest a loop in another, whereas NASM's naming convention makes that process relatively painless.
Re: Problem with number printing function
Posted: Thu Apr 04, 2013 2:27 am
by makuc9
Ah, just a typo. I've read that a lot of times already, so I know. I just wasn't thinking enough about it at the time of posting reply...
Sorry, but thanks for correcting me.
And thanks for explanation. Will have to play a bit with this, than.
