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denial



Joined: 12 Sep 2004
Posts: 98
denial
Hi...

to change the string in a byte array reserved through rb, I always used sprintf from the WinAPI. But as I want to be independent from APIs, I want to use such kind of code from now on:

mov [myvar+0],'A'
mov [myvar+1],'B'
mov [myvar+2],'C'
...

Well its pure and simple, and thus I thought its also fast in execution. But I wanted to know: Is there a way that gets executed faster?

And for copying a string from one var into another, I use this:

mov al,[srcvar+0]
mov [destvar+0],al
mov al,[srcvar+1]
mov [destvar+1],al

How can this be made faster in execution?

Thank you...
Post 27 Oct 2005, 10:19
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7752
Location: Kraków, Poland
Tomasz Grysztar
There are String operation instructions for such purposes.
Post 27 Oct 2005, 10:41
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denial



Joined: 12 Sep 2004
Posts: 98
denial
thank you. how could i forget about them. Embarassed
i'm sorry...
Post 29 Oct 2005, 12:04
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Reverend



Joined: 24 Aug 2004
Posts: 408
Location: Poland
Reverend
Code:
        push    ecx edi esi
        mov     esi, src
        mov     edi, dest
        mov     ecx, size
        rep     movsb
        pop     esi edi ecx    
You can even optimize it, and use 'movsd' in 32-bit or 'movsq' in 64-bit
Post 01 Nov 2005, 09:29
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okasvi



Joined: 18 Aug 2005
Posts: 382
Location: Finland
okasvi
Reverend wrote:
Code:
        push    ecx edi esi
        mov     esi, src
        mov     edi, dest
        mov     ecx, size
        rep     movsb
        pop     esi edi ecx    
You can even optimize it, and use 'movsd' in 32-bit or 'movsq' in 64-bit



so which one is it? in code you have movsb... im not at home so i could test it but i want to know before i memorize either one of those... Neutral movsd/movsb...

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Post 11 Nov 2005, 08:12
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Reverend



Joined: 24 Aug 2004
Posts: 408
Location: Poland
Reverend
The version I posted is correct for all strings (of course for correct arguments). But if you know the string you want to copy is of length dividable by 4 (ie. 4, 8, 12, 16, 20, ...) you can use movsd instruction which copies 4 bytes at once. Then you must also divide size by 4:
Code:
;       if we know that size is dividable by 4
        push    ecx edi esi 
        mov     esi, src 
        mov     edi, dest 
        mov     ecx, size / 4
        rep     movsd
        pop     esi edi ecx    
Post 12 Nov 2005, 14:43
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El Tangas



Joined: 11 Oct 2003
Posts: 120
Location: Sunset Empire
El Tangas
And remember to align memory variables, for example dword variables should be in addresses divisible by 4 (use the "align" keyword in fasm). This is very important for good performance.
Post 13 Nov 2005, 20:58
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