lstrcat replacement

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jochenvnltn

Joined: 15 Jul 2011
Posts: 86

jochenvnltn

Hello everyone ;)

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. I have found a replacement for lstrlen and it works perfect. Im just wondering if i can have that for lstrcat to?

many thanks before hand

05 Dec 2012, 20:34

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

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

05 Dec 2012, 20:42

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4633
Location: Argentina

LocoDelAssembly

BTW, if you need full compatibility, you need to add "mov eax, [lpString1]" just before ret.

05 Dec 2012, 20:57

jochenvnltn

Joined: 15 Jul 2011
Posts: 86

jochenvnltn

LocoDelAssembly wrote:

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    

Interesting.. thank you ill study this Wink

05 Dec 2012, 20:59

mindcooler

Joined: 01 Dec 2009
Posts: 423
Location: Västerås, Sweden

mindcooler

jochenvnltn wrote:

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

jochenvnltn wrote:

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

These statements are contradictory. Why not use StringCchCat?

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05 Dec 2012, 22:40

AsmGuru62

Joined: 28 Jan 2004
Posts: 1423
Location: Toronto, Canada

AsmGuru62

Too many stdcall's!
Smile

Code:

;
; 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

05 Dec 2012, 22:42

jochenvnltn

Joined: 15 Jul 2011
Posts: 86

jochenvnltn

Dont know what to say.. Works perfect! This i will be using all the time!
You realy are a AsmGuru Wink

Code:

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

06 Dec 2012, 15:52

f0dder

Joined: 19 Feb 2004
Posts: 3170
Location: Denmark

f0dder

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

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06 Dec 2012, 16:12

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

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

Description:		Download
Filename:	STRING.INC
Filesize:	21.22 KB
Downloaded:	118 Time(s)

06 Dec 2012, 17:06

jochenvnltn

Joined: 15 Jul 2011
Posts: 86

jochenvnltn

marcinzabrze12 wrote:

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

wow! thank you for this share! it looks very nice..

06 Dec 2012, 17:51

jochenvnltn

Joined: 15 Jul 2011
Posts: 86

jochenvnltn

I just love this code snips! 1000x thank you!

06 Dec 2012, 17:58

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

Please report me if find some bug.

06 Dec 2012, 18:52

jochenvnltn

Joined: 15 Jul 2011
Posts: 86

jochenvnltn

marcinzabrze12 wrote:

Please report me if find some bug.

hello marcinzabrze12.. No! No bug's whatsoever.. Is you gmail in the source still valid? Ill use that to contact you then.. Agian.. thank you..

06 Dec 2012, 22:16

jochenvnltn

Joined: 15 Jul 2011
Posts: 86

jochenvnltn

f0dder wrote:

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

Is (most likely) = Definitely? Because i needed this call multiple times in my code, so your gona say it's slower then the original API import? Im not an expert so please prove your point because im still learning .. and yes.. i have nothing better to do for now Smile

07 Dec 2012, 01:08

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

@f0dder:
Look at implementation of lstrcatA function (kernel32.dll) in AIDA.
lstrcatA is slower than ansiCat (from STRING.INC).
; -----------------------------------------------------------------

If yor code will work on Intel Core i5 or higher than you have specjal assembly instructions "PCMP(x)STR(y)" to do everything with a string data.

07 Dec 2012, 17:25

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 17932
Location: In your JS exploiting you and your system

revolution

f0dder wrote:

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

Are you sure? In general the APIs will be written to handle the average case reasonably efficiently. With "average" being defined by MS in an unknown way. I would doubt that the average case applies perfectly to everyone's usage. Plus the API will likely have extra generic overheads that a custom implementation might not need.

08 Dec 2012, 04:59

yoshimitsu

Joined: 07 Jul 2011
Posts: 96

yoshimitsu

The WinAPI version is implemented in the easiest way you can think of (loop and check for zero), it's actually pretty slow, but small (keeping kernel32.dll small).

Implementing your own function to save space is not really smart.
You're very likely already importing kernel32.dll's functions and adding lstrcat to them takes only a few bytes.

If you want speed and a small executable, you should import from msvcrt.dll instead.
These functions are optimized for speed and process multiple data at a time.

08 Dec 2012, 19:14

marcinzabrze12

Joined: 07 Aug 2011
Posts: 60

marcinzabrze12

Quote:

Implementing your own function to save space is not really smart

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

Quote:

(loop and check for zero)

one JMP on every checked byte - what if you processing 500 KB text file ?
For this reason are instructions like movs* scas* ...

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

09 Dec 2012, 00:37

AsmGuru62

Joined: 28 Jan 2004
Posts: 1423
Location: Toronto, Canada

AsmGuru62

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.

09 Dec 2012, 13:00

f0dder

Joined: 19 Feb 2004
Posts: 3170
Location: Denmark

f0dder

revolution wrote:

f0dder wrote:
2) (most likely) using a slower piece of code than the API version
Are you sure?

Nope, hence why I added the "(most likely)" part Smile

. But you're right, took a look at kernel32, and it was pretty bad - basically two strlen loops and a memcpy (inline code blocks, not function calls, but still).

marcinzabrze12 wrote:

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

Then you should neither use the Windows APIs nor any of the pieces of code posted in this thread so far Smile

marcinzabrze12 wrote:

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

fast != small - often, fast ends up having a fair amount of code.

marcinzabrze12 wrote:

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

Which on some CPUs are quite a lot slower than manually unrolled loops that check several bytes at a time.

AsmGuru62 wrote:

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.

+1.

And if you must deal with zero-terminated strings, I'd suggest at least moving to some safer routines than the libc ones... unless you absolutely, entirely and positively know what the input string lengths will be Smile

09 Dec 2012, 13:31

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