Converting from NASM to FASM, help required!

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SomeoneNew

Joined: 12 Aug 2006
Posts: 54

SomeoneNew 02 Dec 2007, 05:04

Hi guys, I'm attempting to convert from NASM to FASM but I'm new to both so... there you go, I'm stuck since the beginning; Would anybody here be able to help me out on this one?

First, the macros; heres one from NASM:

Code:

%macro getbitM 0
    add    dx, dx
    jnz    short %%stillbitsleft
    mov    dx, [esi]
    lea    esi, [esi + 2]
    adc    dx, dx
  %%stillbitsleft:
%endmacro

How would I go about converting this one to FASM?

Secondly, is this the same in both assemblers?

NASM:

Code:

jae    near .donedepacking

Code:

 jnc    short .literal

What does "near" and "short" mean?, what are they?.

Thanks!

_________________
Im new, sorry if I bothered with any stupid question Smile

02 Dec 2007, 05:04

dosin

Joined: 24 Aug 2007
Posts: 337

dosin 02 Dec 2007, 05:27

A short is a unsigned WORD or SWORD..

near address
A memory location specified by the offset from the start of the value in a segment register. A near address requires only 2 bytes.

macro getbitM 0
add dx, dx
jnz stillbitsleft ;jump if not zero
mov dx, [esi]
lea esi, [esi + 2]
adc dx, dx
stillbitsleft:
endmacro

as for the rest it should be fine- if not look under the macro section..
I don't use macros...I am not sure if the macro getbitM 0 needs to be mod.. Very Happy

02 Dec 2007, 05:27

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 02 Dec 2007, 05:30

Code:

; I'm suppossing that the "0" is a typo
macro getbitM
{
; I'm assuming that a label that starts with %% is local to the macro. 
; I added two dots to not affect the scope of possible surrounding labels

local ..stillbitsleft 
    add    dx, dx 
    jnz    short ..stillbitsleft 
    mov    dx, [esi] 
    lea    esi, [esi + 2] 
    adc    dx, dx 
  ..stillbitsleft: 
}

short is to ensure that the offset will be short (1 byte), and near just specifies that the operand is an offset only so there will be no changes at CS register. http://flatassembler.net/docs.php?article=manual#1.2.5

If you know NASM already I suggest reading the fasm manual anyway since the syntax shares some aspects with NASM but is not 100 % compatible.

02 Dec 2007, 05:30

SomeoneNew

Joined: 12 Aug 2006
Posts: 54

SomeoneNew 02 Dec 2007, 05:50

Thanks, I ported the entire code now and it compiles just fine but I don't have a way to try it out.

I have 2 problems

1) I don't know how to use file io in FASM, how can I read the contents of a file to memory and how can I write the contents of a memory area to a file? - I'm under Windows by the way.

2) How can I convert a "flat" source (ie no procedures, just labels) to a routine / proc ?

Any procedure examples would be great, I just need to return 1 variable.

02 Dec 2007, 05:50

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7105
Location: Slovakia

vid 02 Dec 2007, 10:44

Quote:

I don't know how to use file io in FASM, how can I read the contents of a file to memory and how can I write the contents of a memory area to a file? - I'm under Windows by the way.

many ways:
Win32API - CreateFile(), ReadFile(), WriteFile()
libc (msvcrt.dll) - fopen(), fread(), fwrite()
FASMLIB

Quote:

How can I convert a "flat" source (ie no procedures, just labels) to a routine / proc ?

best way is with "proc" macro - review FASM documentation of win32 headers (click "documentation" on FASM site)

02 Dec 2007, 10:44

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