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LeglessQuasimodo
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 Posted: Mon Aug 31, 2015 6:10 am Post subject: Clarifications needed |
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hello there,slowly learning CE,atm I using MG:GZ as a learning base
1- Question
I have changed my max ammo using 4 bytes which was easy considering the value in game was the same in cheat engine,but this was not true for the ammo clip,a total of 8 ammo was being show 7 in cheat engine,and 7 in-game as being 6 in cheat engine,why is this?
2 - Question
Using someone else table to learn,I was able to learn how to make a no-reloaded script,the problem is only the first part I could understand,the second part was a total nonsense to me,and am additional xmm1 which I don't know where the hell that come from
this is what I gathered
| Code: |
newmem:
movss xmm1,[rcx+00000450] //mov xmm1 to max ammo clip
movss [rcx+0000044C],xmm1 //mov current ammo clip to max ammo clip (xmm1)
originalcode:
mov eax,[rcx+0000044C]
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original code is mov [rcx+0000044C],eax instead of mov eax,[rcx+0000044C],why it was to be changed?
and why movss instead of mov,and xmm1 instead of eax
the table is working,but I don't to use it before I actually understand why the changes,thanks in advance.
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Stregum
Advanced Cheater
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Joined: 17 Jun 2014
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Location: We make baguettes there !
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| Posted: Mon Aug 31, 2015 6:39 am Post subject: |
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Hey
1.
It's the developer choice to make the ammo system, the value is shifted by one right ? so an empty magazine would have a value of -1 (probably) instead of zero, that's reasonable, it's the way the game is coded.
2.
I wanna get your attention here:
"mov x,y"
actually means
"x = y" and not "y = x"
x<<y if you prefer
mov and movss are the same kind of instruction, but movss is for floats (floating point value)
xmm1 is a register that can contain some floats or doubles.
So what it does;
| Code: |
newmem:
movss xmm1,[rcx+00000450] //Store the max ammo clip into a temporary register (remember, right to left, so xmm1 takes the value of [rcx+450]
movss [rcx+0000044C],xmm1 //Set the current ammo clip to the value stored in xmm1, which is max ammo.
originalcode:
mov eax,[rcx+0000044C]
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The idea is to do:
| Code: |
[PseudoCode]
currentAmmo = maxAmmo
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But since you can't do memory to memory modification like
| Code: |
mov [rcx+00000450],[rcx+0000044C] //WONT WORK !!
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A intermediate register must be used, and this is where xmm1 comes in, and does a bridge between 2 memory values.
And for your question:
eax is probably your decreased ammo value, it is your current ammo decreased by 1, and the new xmm1 is the max ammo for your brand new filled clip. 
_________________
Rhaa Stregum Vitae
Last edited by Stregum on Mon Aug 31, 2015 8:32 am; edited 1 time in total |
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LeglessQuasimodo
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| Posted: Mon Aug 31, 2015 7:50 am Post subject: |
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so reading your answer I have this
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newmem:
movss xmm0,[rcx+00000450] //store max ammo clip into a temporary register (temp register < max ammo)
movss [rcx+0000044C],xmm0 //set current ammo clip to temporary register (current ammo > temp register/max ammo)
originalcode:
mov eax,[rcx+0000044C] //decrease < current ammo/temporary register(xmm0)
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is this about right or there is anything off that I need to know/understand?
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Stregum
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Location: We make baguettes there !
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| Posted: Mon Aug 31, 2015 8:24 am Post subject: |
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Wrong ! :p (I don't know if it's a typo you've made)
| Code: |
movss [rcx+0000044C],xmm0 //set current ammo clip to temporary register (current ammo > temp register/max ammo)
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Right !
| Code: |
movss xmm0,[rcx+00000450] //store max ammo clip into a temporary register (temp register < max ammo)
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So, what you need to understand is whatever there is on the right or left parameters (x and y in the above example) in mov instructions*, this is always the same way of handling these instructions, from right to left**.
(Do you know what "[rcx+###]" means btw ?)
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mov x,y // x < y , WHATEVER THE x AND y ARE
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So, as mentionned, this
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movss [rcx+0000044C],xmm0 //set current ammo clip to temporary register (current ammo > temp register/max ammo)
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should be this
| Code: |
movss [rcx+0000044C],xmm0 //set current ammo clip to temporary register (current ammo <<<<<<<<<<<< temp register/max ammo)
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this doesn't changes anything in the code, but you're interpretation is wrong, it's still right to left.
As for this
| Code: |
originalcode:
mov eax,[rcx+0000044C]
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I don't think it is needed, you could try to erase this part (don't forget to erase the label(originalcode) declaration if it works), if it crashes I guess it's probably necessary ^.^
__________________________________
*There are other instructions that does that, such as
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add x,n (x = x + n) : add eax,3
sub x,n (x = x - n) : sub ecx,4C
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The list is way longer than that, but it's so you can understand what i mean
**I don't want to confuse you, currently, you're writing in Intel syntax, but there is an other notation called "AT&T", that reverses the order
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mov %eax,%ebx //eax > ebx
sub $C,%esp // esp = esp - 0xC
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But you don't have to care neither about the notation nor the $ and % symbols, it's just so you don't blame me if you read that somewhere else ^^
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Rhaa Stregum Vitae |
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LeglessQuasimodo
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| Posted: Mon Aug 31, 2015 8:57 am Post subject: |
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fixed it,thank you.
| Code: |
movss xmm0,[rcx+00000450] //store max ammo clip into a temporary register (temp register < max ammo)
movss [rcx+0000044C],xmm0 //set current ammo clip to temporary register (current ammo < temp register/max ammo)
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but I still need some info on this one,to make sure I get it right.
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mov eax,[rcx+0000044C] //decrease < current ammo/temporary register(xmm0)
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[rcx+0000044C] being xmm0,does this mean that eax will now be handled as xmm0 (decrease ammo < xmm0/current/max ammo) ??
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Stregum
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Joined: 17 Jun 2014
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Location: We make baguettes there !
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| Posted: Mon Aug 31, 2015 9:11 am Post subject: |
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| Quote: |
[rcx+0000044C] being xmm0,does this mean that eax will now be handled as xmm0 (decrease ammo < xmm0/current/max ammo) ??
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eax = xmm0, yes, if that's what you mean.
That's why I don't think this mov is necessary, but we never know..
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Rhaa Stregum Vitae |
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Zanzer
I post too much
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| Posted: Mon Aug 31, 2015 5:49 pm Post subject: |
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Assuming the value is 4-byte and you're using XMM1 for no reason, it sounds like the code you want is.
| Code: | mov eax,[rcx+00000450] // move max ammo into EAX
dec eax // decrease by 1, because you said that's how it's stored
mov [rcx+0000044C],eax // move max ammo minus 1 into current ammo |
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Stregum
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Location: We make baguettes there !
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| Posted: Thu Sep 03, 2015 3:39 pm Post subject: |
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The xmm1 register didn't make sense to me either, but it was in his code, oddly
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