proc lstrcat uses esi edi, lpString1, lpString2
  mov edi, [lpString1]
  stdcall lstrlen, edi

  add edi, eax

  mov esi, [lpString2]
  stdcall lstrlen, esi
 
  lea ecx, [eax + 1]
  rep movsb

  ret
endp    

To not steal from you the opportunity to do it the efficient way, I'll implement it in the laziest way possible, taking advantage of your lstrlen replacement:

Code:

proc lstrcat uses esi edi, lpString1, lpString2
  mov edi, [lpString1]
  stdcall lstrlen, edi

  add edi, eax

  mov esi, [lpString2]
  stdcall lstrlen, esi
 
  lea ecx, [eax + 1]
  rep movsb

  ret
endp    

Im trying to write a program in fasm and keep it as small as i can.

Does anyone know a lstrcat replacement. Because i dont want to imort the API unless there is no other way.

;
; INPUT:
;   EDI = destination buffer
;   ESI = source buffer
; OUTPUT:
;   EAX = points to a null terminator in destination buffer
;   ( ^^^ in case of more concatenations to follow)
;
StrCat:
   push    ecx esi edi
 xor     eax, eax
    or      ecx, -1
     repne   scasb

   dec     edi

.more:
       lodsb
       stosb
       test    eax, eax
    jnz     .more

   lea     eax, [edi - 1]
      pop     edi esi ecx
 ret
    

format pe gui 4.0
include 'win32ax.inc'

str1 db 'hello ',0
str2 db 'world!',0

dest dd ?

start:

        mov esi,str2
        mov edi,str1
        call StrCat

        invoke MessageBox,0,str1,'caption',MB_OK
        invoke ExitProcess,0

; StrCat Replacement
; fuck shit with Too many stdcall's!  By AsmGuru62 (.flatassembler.net)
; INPUT:
;   EDI = destination buffer
;   ESI = source buffer
; OUTPUT:
;   EAX = points to a null terminator in destination buffer
;   ( ^^^ in case of more concatenations to follow)
;
StrCat:

        push    ecx esi edi
        xor     eax, eax
        or      ecx, -1
        repne   scasb

        dec     edi

.more:
        lodsb
        stosb
        test    eax, eax
        jnz     .more

        lea     eax, [edi - 1]
        pop     edi esi ecx
        ret

.end start
    

Dont know what to say.. Works perfect! This i will be using all the time!

Check this and change to without 'proc / endproc' if you want.

Please report me if find some bug.

jochenvnltn wrote:

Dont know what to say.. Works perfect! This i will be using all the time!

So, to avoid an import you're
1) adding more bytes to your executable and
2) (most likely) using a slower piece of code than the API version

2) (most likely) using a slower piece of code than the API version

Implementing your own function to save space is not really smart

(loop and check for zero)

f0dder wrote:

2) (most likely) using a slower piece of code than the API version

Are you sure?

I don't need to save space. I need to improve speed.

I looked now in AIDA disasembled code of msvcrt.dll "strlen", "strcmp" ... is not fast and is not that small.

For this reason are instructions like movs* scas* ...

If your code has a lot of string concatenations you may want to think of developing your own string library where you always know the string length, like Pascal does. This way your concatenation code will omit the code searching for null terminator and it will perform even faster.