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Convert C code to Assembly code

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Join Date: May 2008

Posts: 1

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guneky

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Convert C code to Assembly code

May 2nd, 2008

Hello, I tried to convert below code, but I couldn't.. What is wrong?

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
void invert(unsigned char *image, int width, int height){
         for(int i=0;i<width*height;i++)
               image[i]=255-image[i];
}
void invert(unsigned char *image, int width, int height){
         for(int i=0;i<width*height;i++)
               image[i]=255-image[i];
}

 Help with Code Tags 
 assembly Syntax (Toggle Plain Text) 
---------------------ASM---------
invert PROC
	push ebp					; save ebp register
	mov ebp,esp					; get current stack pointer
 
	mov esi,[ebp+8]				; get first parameter
	mov eax,[ebp+12]			; get second parameter
	mov ebx,[ebp+16]			; get third parameter
	mul ebx						; eax=eax * ebx
	mov ecx,eax					; get image size
	dec ecx
	mov al,255
 
	L1:
		sub al,[esi]			; al=al-image[i]
		mov [esi],al			; image[i]=al
		inc esi
		loop L1
 
	pop ebp						; restore ebp
	ret							; return to caller
 
invert ENDP
---------------------ASM---------
invert PROC
	push ebp					; save ebp register
	mov ebp,esp					; get current stack pointer
	
	mov esi,[ebp+8]				; get first parameter
	mov eax,[ebp+12]			; get second parameter
	mov ebx,[ebp+16]			; get third parameter
	mul ebx						; eax=eax * ebx
	mov ecx,eax					; get image size
	dec ecx
	mov al,255
	
	L1:
		sub al,[esi]			; al=al-image[i]
		mov [esi],al			; image[i]=al
		inc esi
		loop L1
	
	pop ebp						; restore ebp
	ret							; return to caller
	
invert ENDP

--------------------------------------------------
please help me....thanks...

Last edited by Ancient Dragon; May 2nd, 2008 at 4:54 pm. Reason: add code tags

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Join Date: Feb 2005

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Tight_Coder_Ex Tight_Coder_Ex is offline

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Re: Convert C code to Assembly code

May 3rd, 2008

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Originally Posted by guneky

Hello, I tried to convert below code, but I couldn't..

Actually that's not correct, you did convert it and a reasonably good job too, the only problem is it's not working as expected.

1. You only initialize AL to -1 (255 or 0FFH) once and then inside your loop it's modified.

 Help with Code Tags 
 asm Syntax (Toggle Plain Text) 
L1:    push    eax
         sub      al, [esi]
         stosb
         pop     eax
         loop    L1
L1:    push    eax
         sub      al, [esi]
         stosb
         pop     eax
         loop    L1