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Index > Windows > Problem with inc instruction.

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Barf



Joined: 17 Sep 2004
Posts: 34
Location: Poland
Barf
I have such code:
Code:
 .NotMatch:
    mov ch, [esi]
    xor ch, 0
    inc esi
    jnz .NotMatch    

And it doesn't work (when it's ran Windows returns error). if I replace "inc esi" before "mov ch, [esi]" it works. Does anybody have any idea, why? And how can I repair that without adding dec before loop and replacing "inc esi"?
Post 13 Apr 2006, 09:07
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madmatt



Joined: 07 Oct 2003
Posts: 1045
Location: Michigan, USA
madmatt
I think you need to do something like swap the inc esi and xor ch, 0.
Code:
.NotMatch
  mov ch, [esi]
  inc esi
  xor ch, 0
  jnz .NotMatch    
Post 13 Apr 2006, 09:21
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Barf



Joined: 17 Sep 2004
Posts: 34
Location: Poland
Barf
it still doesn't work...
Post 13 Apr 2006, 09:53
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shoorick



Joined: 25 Feb 2005
Posts: 1608
Location: Ukraine
shoorick
not clear what are you doing with "xor ch,0"? it will not change ch. ZF will on when ch=0 only, but it is not usual kind of comparing with zero. please, give examples when it should loop, and when it should not.

regards!
Post 13 Apr 2006, 10:15
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Kermil



Joined: 26 Oct 2005
Posts: 35
Location: Russia
Kermil
Incrementation of esi register change ZF flag. In the end of loop try to check up ch register using the "or" command.

Not clear what do you want in this example, but I try to assume, that you want get length of ascii string. Try to use following code:
Code:
.NotMatch:
    mov ch, [esi]
    or   ch, ch
    jz   .Match
    inc esi
    jmp .NotMatch
.Match:
    
Post 13 Apr 2006, 10:34
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Barf



Joined: 17 Sep 2004
Posts: 34
Location: Poland
Barf
ok thanks.
Post 13 Apr 2006, 11:25
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