ASM Community

Hi all. I don't really know if this is the appropriate forum but it could fit here. Anyway I've been trying to write a string removal procedure with the following conditions:

[*]Accepts a pointer to location to remove string
[*]Removes n characters starting at the location

Here's an example:


.data

someString BYTE "1234vvvv5678",0

.code

INVOKE str_remove,ADDR [someString+3],4


That code would instruct the procedure to remove "vvvv". So far I have thought of two methods, both failures:


[*]Starting with the first character to be removed, copy the following byte into the current position and advance the pointer. This, however, results with only the last "v" being replaced with a "5".
[*]Starting with the last character to be removed, copy the following byte into the current position and move the pointer back one.

Does anyone have a method for doing this? I don't want any code (pseudo-code is fine) because I'd like to try and accomplish this myself. I know this is pretty basic, but I've been stuck for quite some time. Any help is greatly appreciated :alright:

Afternoon, DaRetard.

Something like this possibly:

str_remove PROC uses edi esi l_ptrString:DWORD, l_dwLength:DWORD



	mov edi, l_ptrString	; Pointing to start of removal.

	mov esi, l_ptrString

	add esi, l_dwLength	; Pointing to the rest of the string to concatenate.



	@@:

		lodsb		; Load character from esi address; esi incremented to next character.

		stosb		; Store that character at edi address; edi incremented to next character.

	cmp al, 0		; Have we found the terminating zero?

	jnz @B			; Nope, so jump back to do the next character.



	; Substring removed.



	ret

str_remove ENDP

You'd also want to use:

invoke str_remove, ADDR [myStringToTest+4],4

if you wished to remove those vvvv's.
Using

invoke str_remove, ADDR [myStringToTest+3],4

would start the removal at the fourth character, which is '4' in your string.

Cheers,
Scronty

I must be damn slow:grin: . There were no replies to this thread when I started chucking together a solution:( .
At least I was able to create a test proggy to make sure the proc I've shown actually works as intended :alright:

Exit if the string if iStart is beyond the end of the string.

lszCut FRAME pString,iStart,nLen

	

	mov edi,[pString]

	mov esi,edi

	mov ecx,[iStart]

	add esi,ecx

	add esi,[nLen]

	

	xor eax,eax

	repne scasb

	or ecx,ecx

	jz >

		ret

	:

	mov al,[esi]

	mov [edi],al

	inc edi

	inc esi

	or al,al

	jnz <



	mov eax,[pString]

	RET

ENDF

Afternoon, lying viruswriting pirate.

He can always use what we showed to compare with what he himself comes up with.:alright:

Going by my own coding skills, my solution would not be the better algorithm.:sweat:

Cheers,
Scronty

It was easy to follow, and that's somewhat more important than "the best code" when helping people out :alright:.