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Homtaro
How do I cheat?
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Joined: 02 Apr 2022
Posts: 5
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 Posted: Fri Feb 03, 2023 4:49 pm Post subject: Need help dividing 16bit registers |
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So I got back into cheat engine and encountered a problem:
I dont know optimal way to divide registers such as ax,cx etc.
Right now I'm working on script dividing ax in following code:
| Code: |
sub cx,ax
mov eax,[esp+08]
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I could use shr, but I want more precise control, something like using div,[something].
Also if there is good website\guide with such information so I dont ask dumb questions in future, a link would be great.
Any help is appreciated.
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ParkourPenguin
I post too much
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Joined: 06 Jul 2014
Posts: 4702
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| Posted: Fri Feb 03, 2023 5:29 pm Post subject: |
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I'd recommend using floating point math so you can divide by a fractional amount: 1.5 for example.
| Code: | ...
alloc(newmem,4096)
label(divisor)
newmem:
movzx eax,ax
cvtsi2sd xmm0,eax
divsd xmm0,[divisor]
cvttsd2si eax,xmm0
code:
sub cx,ax
mov eax,[esp+08]
jmp return
newmem+800:
divisor:
dq (double)1.5
... |
See any x86-64 instruction set reference manual for information on instructions. Intel has official PDFs on their website, but there are more accessible mirrors:
https://www.felixcloutier.com/x86/
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Dark Byte
Site Admin
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Joined: 09 May 2003
Posts: 25796
Location: The netherlands
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| Posted: Fri Feb 03, 2023 6:06 pm Post subject: |
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You don't have to use floats if you don't want to.
e.g. divide by 1.5: first multiply the value by 10 and then divide it by 15
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Homtaro
How do I cheat?
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Joined: 02 Apr 2022
Posts: 5
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| Posted: Sat Feb 04, 2023 1:15 am Post subject: |
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| Thanks for the information, you guys are lifesavers.
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ParkourPenguin
I post too much
Reputation: 152
Joined: 06 Jul 2014
Posts: 4702
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| Posted: Sat Feb 04, 2023 2:59 am Post subject: |
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Fixed point math is also an option, albeit quite obscure:
| Code: | // divides by 1.5
movzx eax,ax
imul rax,rax,AAAAAAAC
shr rax,32 |
I had to fiddle with a compiler to get this. I'm just pointing out that this exists: don't actually use this in anything.
The benefit of using a float / double is it's easy for the user to change it in the address list. Just use registersymbol to make it accessible.
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