ASM Community

[size=12]InString2 proc uses ebx edi esi, lpSource:DWORD, lpPattern:DWORD[/size]

[size=9]

  ;-------------------------------------------------------------

  ; by Iblis

  ;

  ; InString2 searches for the first occurance of the string

  ; pointed to by lpPattern in the string pointed to by lpSource

  ; and returns the (1) based index into the character array.

  ;

  ; This version of InString does not use a starting position,

  ; so calculating the position is the responsibility of the

  ; user, although adding this functionality wouldn't be too

  ; difficult.  The main purpose of this is to play with an idea

  ; I had about string searching.  Instead of doing a straight

  ; byte scan, the routine creates a simple checksum for the

  ; pattern string and compares it with the source string.  If

  ; the checksums match, one last check is made to see if the

  ; strings match byte for byte.  The idea is that perhaps this

  ; might speed the search up a bit.

  ;

  ; Return value:

  ; On success, the (1) based index of the search string is

  ; returned.  If there is no match, the routine returns (0).

  ; Returns -1 on error.  Possible causes for error include:

  ; -If the pattern string is longer than the source.

  ; -If the pattern string has zero length.

  ;-------------------------------------------------------------[/size]

[size=12]

	mov esi, 	lpSource

	mov edi, 	lpPattern

	xor eax, 	eax

	xor edx, 	edx

@chksm: movzx 		ebx, byte ptr [esi]

	inc 		esi

	movzx 		ecx, byte ptr [edi]

	inc 		edi

	lea 		eax, [eax + ecx]

	lea 		edx, [edx + ebx]

	dec 		bl

	sub 		bl, 0FFh

	not 		ecx

	inc 		ecx

	ja 		 @error

	jnz		 @chksm

	sub 		edx, ebx

	lea 		ecx, [edi - 1]

	sub 		ecx, lpPattern

	jz 		 @error

	sub 		esi, ecx

	dec 		esi

@findm:	cmp 		eax, edx

	je 		 @match

@findn:	movzx 		ebx, byte ptr [esi]

	sub 		edx, ebx

	movzx 		ebx, byte ptr [esi + ecx]

	lea 		edx, [edx + ebx]

	inc 		esi

	or 		ebx, ebx

	jnz 		 @findm

	xor 		eax, eax

	jmp 		 @done

@match:	mov 		edi, lpPattern

	mov 		ebx, ecx

	repe 		cmpsb

	sub 		esi, ebx

	add 		esi, ecx

	or 		ecx, ecx

	mov 		ecx, ebx

	jnz 		 @findn

	lea 		eax, [esi + 1]

	sub 		eax, lpSource

	jmp 		 @done

@error:	mov 		eax, -1

@done:	ret



InString2 endp[/size]

chksm: movzx 		ebx, byte ptr [esi]

	inc 		esi

	movzx 		ecx, byte ptr [edi]

	inc 		edi

	lea 		eax, [eax + ecx]

                lea 		edx, [edx + ebx] 



	dec 		bl

	sub 		bl, 0FFh

	not 		ecx

	inc 		ecx

	ja 		 @error

	jnz		 @chksm