Linux Format forums

Re: Newbie NASM question

M-Saunders — Thu Apr 19, 2012 4:23 pm

Author: M-Saunders

Posted: Thu Apr 19, 2012 4:23 pm

pk_fox wrote:

can't get lib_input_number to play ball

Please be much more specific! Does it not work at all? Does it return the wrong number? What exactly happens? Does the program crash?

pk_fox wrote:

call lib_input_number
mov [looplimit],eax ; is this correct ? where is the converted number held ?

library.asm tells you: "Store positive integer in EAX". Please always read the documentation at the start.

pk_fox wrote:

; modded lib_input_number

How did you modify it? It's very difficult for me to bugfix something when you've changed the routines and not described how...

M

Re: Newbie NASM question

pk_fox — Thu Apr 19, 2012 1:14 pm

Author: pk_fox

Posted: Thu Apr 19, 2012 1:14 pm

pk_fox wrote:

M-Saunders wrote:

Ah yes, the limit was due to using word sizes. Change this bit of the code (in lib_print_number):

Code:

mov eax, 0 ; Start converting number to ASCII
mov word ax, [loopctr]

to just:

Code:

mov dword eax, [loopctr]

As for passing the limit as a parameter, yep, that's also doable. But bear in mind that the limit number will be passed as an ASCII text string, so you can't use it directly. Instead, you need to convert it from a string to a proper number; there's code for this in lib_input_number in library.asm.

Give it a try, good luck, and let me know if you need any help!

M

Cheers Mike, I do appreciate your help, how do you know what registers to put what in ( if that makes sense ) I've downloaded a few articles from the web and none of them state in muppet terms "this must go in eax","this must be a dword" etc etc... I'm finding it difficult to self help ( I'm sure you dont want me bugging you every day ) ]'m a pro dev of long standing but never got involved with assembler as I never had a need to ( nor do I now but it's fascinating ) keep up the tutorials !!

Me again !, can't get lib_input_number to play ball this is what I've tried

_start:
mov dword [loopctr],0
;mov dword [looplimit],100
pop ebx ; argc (argument count)
pop ebx ; argv[0] (argument 0, the program name)
pop ebx ; The first real arg, a filename
mov [filename],ebx
pop ebx ; extra pop for looplimit param
mov [buffer],ebx ; then move it to your buffer var
call lib_input_number
mov [looplimit],eax ; is this correct ? where is the converted number held ?
mov ebx,[filename]

; rest of the code unchanged.

; modded lib_input_number

lib_input_number:
pusha

;mov edi, buffer ; already populated by me
;call lib_input_string ; don't need this call ?

mov esi, buffer ; buffer has the last popped ebx

mov eax, 0 ; Initialise accumulator
mov ebx, 10 ; Decimal-system's radix

.next_digit:
mov cl, [esi] ; Fetch next character
cmp cl, '0' ; Char preceeds '0'?
jb .invalid ; Yes, not a numeral
cmp cl, '9' ; Char follows '9'?
ja .invalid ; Yes, not a numeral
mul ebx ; Ten times prior sum
and ecx, 0x0F ; Convert char to int
add eax, ecx ; Add to prior total
inc esi ; Advance source index
jmp .next_digit ; And check another char

.invalid:
mov long [tmp], eax ; Get EAX back after popa
popa
mov long eax, [tmp]
ret

sorry to be a pain

Re: Newbie NASM question

M-Saunders — Thu Apr 19, 2012 12:39 pm

Author: M-Saunders

Posted: Thu Apr 19, 2012 12:39 pm

pk_fox wrote:

That's impossible to say -- it depends entirely what you want to do. All good routines and libraries should document which registers they use to receive data, and which registers they use to pass data back. For instance, the comment section at the top of library.asm tells you which registers are used by the corresponding routines.

M

Re: Newbie NASM question

pk_fox — Thu Apr 19, 2012 7:52 am

Author: pk_fox

Posted: Thu Apr 19, 2012 7:52 am

M-Saunders wrote:

Ah yes, the limit was due to using word sizes. Change this bit of the code (in lib_print_number):

Code:

mov eax, 0 ; Start converting number to ASCII
mov word ax, [loopctr]

to just:

Code:

mov dword eax, [loopctr]

Re: Newbie NASM question

M-Saunders — Wed Apr 18, 2012 4:22 pm

Author: M-Saunders

Posted: Wed Apr 18, 2012 4:22 pm

Ah yes, the limit was due to using word sizes. Change this bit of the code (in lib_print_number):

Code:

mov eax, 0 ; Start converting number to ASCII
mov word ax, [loopctr]

to just:

Code:

mov dword eax, [loopctr]

Re: Newbie NASM question

pk_fox — Wed Apr 18, 2012 2:50 pm

Author: pk_fox

Posted: Wed Apr 18, 2012 2:50 pm

M-Saunders wrote:

OK, here is a version with lib_print_number included from library.asm, and modified slightly to use the file descriptor. I've marked the additional lines with "XXX" in the comments:

http://pastebin.com/hNQjZE8R

This puts the number before each line in the file. Any questions, just shout!

M

Hi Mike, thanks very much for your help, one thing I notice is, if I change looplimit to 1000000 the last line in my output file is only 16959 ) Hello, world! - what do I need to change to use larger values ? also I would like to pass the limit as a parameter - is this possible ?

Re: Newbie NASM question

M-Saunders — Wed Apr 18, 2012 1:32 pm

Author: M-Saunders

Posted: Wed Apr 18, 2012 1:32 pm

OK, here is a version with lib_print_number included from library.asm, and modified slightly to use the file descriptor. I've marked the additional lines with "XXX" in the comments:

http://pastebin.com/hNQjZE8R

This puts the number before each line in the file. Any questions, just shout!

M

Re: Newbie NASM question

pk_fox — Tue Apr 17, 2012 9:59 am

Author: pk_fox

Posted: Tue Apr 17, 2012 9:59 am

M-Saunders wrote:

OK, you probably need to change the output stream. Put your current code into pastebin.com and I'll have a look at it!

M

Hi Mike, never used pastebin before, I've put the code there and called it Code for Mike Saunders

Thanks again

Re: Newbie NASM question

M-Saunders — Mon Apr 16, 2012 1:18 pm

Author: M-Saunders

Posted: Mon Apr 16, 2012 1:18 pm

OK, you probably need to change the output stream. Put your current code into pastebin.com and I'll have a look at it!

M

Re: Newbie NASM question

pk_fox — Mon Apr 16, 2012 12:49 pm

Author: pk_fox

Posted: Mon Apr 16, 2012 12:49 pm

M-Saunders wrote:

Ah. In that case you'll need a routine to convert a numeric value into its printable ASCII equivalent, and then print it. If you've got LXF156, the lib_print_number routine in library.asm does the trick. If not, I can post it here...

M

Hi Mike, tried using your print_number code with no success, If I'm reading it correctly your routine expects the number to be printed to be in eax, so I
*pushed eax* , *moved my value into eax* , called your routine then *popped eax* ; end result utter garbage in my output file I am outputting to a file not the screen

Re: Newbie NASM question

pk_fox — Mon Apr 16, 2012 9:32 am

Author: pk_fox

Posted: Mon Apr 16, 2012 9:32 am

M-Saunders wrote:

Hi Mike, I downloaded the lib code and note that your routine prints to the screen and also adds a newline but I'm going to have a go modifying the code for my needs, thanks again and keep the helpline open

Re: Newbie NASM question

pk_fox — Mon Apr 16, 2012 8:39 am

Author: pk_fox

Posted: Mon Apr 16, 2012 8:39 am

Thanks Mike , slight problem I've got the mag but not the dvd which has the code

Re: Newbie NASM question

M-Saunders — Sun Apr 15, 2012 11:03 pm

Author: M-Saunders

Posted: Sun Apr 15, 2012 11:03 pm

Ah. In that case you'll need a routine to convert a numeric value into its printable ASCII equivalent, and then print it. If you've got LXF156, the lib_print_number routine in library.asm does the trick. If not, I can post it here...

M

Re: Newbie NASM question

pk_fox — Sat Apr 14, 2012 12:39 pm

Author: pk_fox

Posted: Sat Apr 14, 2012 12:39 pm

M-Saunders wrote:

What do you mean by line number here -- ie referring to which file?

M

Hi Mike, sorry for not being clear. at the moment I write this string x times
' ) Hello, world!', what I would like to do is:

'1 ) Hello, world!'
' 2 ) Hello, world!'
'3 ) Hello, world!'
etc...

your tutorials started all this good fun though

Re: Newbie NASM question

M-Saunders — Sat Apr 14, 2012 12:12 pm

Author: M-Saunders

Posted: Sat Apr 14, 2012 12:12 pm

What do you mean by line number here -- ie referring to which file?

M