Simple application i cant workout

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jacko221

Joined: 12 Nov 2005
Posts: 22

jacko221 19 Nov 2005, 10:01

Hi every one, i was reading up on jump statments and wanted to make a simple program which compares 2 variables and shows a messageBox depending on which value. The code is below.

Code:

include 'C:\fasmw164\INCLUDE\win32ax.inc'

msgBoxCaption  db   '???',0
msgBoxText     db   'Not Equal too',0
msgBoxText1    db   'Equal too',0


mov ax, 10
mov bx, 10
cmp ax,bx
jne start
jmp start1

start:
          push MB_OK
          push msgBoxCaption
          push msgBoxText
          push NULL
          call [MessageBox]
          jmp exitP
.end start ; Here is the problem





     start1:

          push MB_OK
          push msgBoxCaption
          push msgBoxText1
          push NULL
          call [MessageBox]
          jmp exitP
          
exitP:
invoke ExitProcess,0

The problem is that if i remove ".end start" the program will not assemble. But i leave it the way it is (with it in the code) then jne goes directly to "start:" even though the two values are equal (ax, bx both equal 10).
Could any one help me out with this problem? I'd really appreciate it.

P.S
Sorry if im speaking kinda weird crap cause im only beginning and i don't really know that much about ASM.

Thanks in advance, Jack.

19 Nov 2005, 10:01

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 19 Nov 2005, 13:44

Take in mind that the execution of the program begins at "start:" or the label you put in ".end" which is "start" in this case.

This will work:

Code:

include 'C:\fasmw164\INCLUDE\win32ax.inc' 

msgBoxCaption  db   '???',0 
msgBoxText     db   'Not Equal too',0 
msgBoxText1    db   'Equal too',0 

start:
mov ax, 10 
mov bx, 10 
cmp ax,bx 
jne start2
jmp start1 

start2: 
          push MB_OK 
          push msgBoxCaption 
          push msgBoxText 
          push NULL 
          call [MessageBox] 
          jmp exitP 


     start1: 

          push MB_OK 
          push msgBoxCaption 
          push msgBoxText1 
          push NULL 
          call [MessageBox] 
          jmp exitP 
           
exitP: 
invoke ExitProcess,0

.end start ; Put this always at the end of the code. Check .end macro in win32ax.inc to see why

19 Nov 2005, 13:44

jacko221

Joined: 12 Nov 2005
Posts: 22

jacko221 20 Nov 2005, 04:27

thank you very much locodelassembly, i will look up on macro and find out more about it. Hopefully it will help me when i make w32 applications.

Thanks again Jack.

20 Nov 2005, 04:27

jdawg

Joined: 26 Jun 2005
Posts: 39

jdawg 03 Dec 2005, 21:06

Here are two macros I use for min and max that could help. Though I'm sure if you asked one of the senoir members you could get more effecient ones.

Code:

macro min a,b
{
    mov    eax,a
    mov    ecx,b
    cmp    eax,ecx
    jg       RetB       ;return b (in eax) if eax<ecx
    jmp    finish
  RetB:
   mov    eax,b
  finish:
}

macro max a,b
{
   mov    eax,a
   mov    ecx,b
   cmp    eax,ecx
   jl        RetB      ;return b (in eax) if eax>ecx
   jmp    finish
 RetB:
   mov   eax,b
 finish:
}

They look the same, but notice the subtle "jg" and "jl". That's all it takes. The pros probably know a better way though.

03 Dec 2005, 21:06

r22

Joined: 27 Dec 2004
Posts: 805

r22 04 Dec 2005, 06:29

If your processor supports cmovXX instructions (most do now)
;;Unsigned min
mov eax, a
mov ecx, b
cmp eax,ecx
cmova eax,ecx
;;Unsigned max
mov eax, a
mov ecx, b
cmp eax,ecx
cmovb eax,ecx

;;Signed min
mov eax, a
mov ecx, b
cmp eax,ecx
cmovg eax,ecx
;;Signed max
mov eax, a
mov ecx, b
cmp eax,ecx
cmovl eax,ecx

I used to like the novell SBB AND ADD method but after benchmarking using CMOV is fastest.

04 Dec 2005, 06:29

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