Cheat Engine

PrometheusPB · How do I cheat? Reputation: 0 Joined: 01 Apr 2018 Posts: 5

(I hope I posted this in the right place, if not, sorry moderator(s))

So I am hacking a program and I find the instruction I was looking for, but the code was a bit odd. I haven't run into this before, so it got me to thinking...

As follows:

00534083 - 83 00 FF - add dword ptr [eax],-01

Would that not literally be equivalent to:

00534083 - 83 00 01 - sub dword ptr [eax],01

It is obviously a signed byte (as I have tried changing it to -80 [hex] and it did not fit, but -7F [hex] did), but what is the difference between the two? Is there some benefit to add -1 as opposed to subtracting 1? Is that not the same instruction with a different operand? Anyone know why this was coded to add -1 instead of simply subtracting 1?

Is this some sort of tin-foil hat conspiracy, or is it just wacky coding that is as wacky as the game itself? Developer trolling? I tried it both ways and it works the same, so why do it that way? Any ideas, because maybe I missed something here?

I'm a bit new to ASM, so I don't understand the relevance of one over the other. This code came from the compiled result of the Torque Game Engine (I can't find it either), if that means anything to anyone.

Just curious if there was some reason for this method.

Anyone?

ParkourPenguin · Posted: Wed Apr 04, 2018 9:14 am Post subject:

There's not much difference between adding -1 and subtracting 1. Given the same input, some flags are different between the two (i.e. CF / AF). There might be negligible performance differences between the two.

It was probably either explicitly written that way in the source code or it was compiled that way just because.

PrometheusPB · How do I cheat? Reputation: 0 Joined: 01 Apr 2018 Posts: 5

Thanks for the input...That is much food for thought, I'll have to hit the books a little more. I might have mixed up the ASM bytes a bit, but I follow where you are going. I still get a bit confused on syntax sometimes, like when I see one register following another ([eax,esi] for a crude example... "is it push eax into esi?, no it's push esi to eax...gaah! it's too early in the morning, where's my beer? rofl). I'm working on it, eventually.

I clearly still have much to learn, which is sometimes difficult for me after my compact car was converted into a sub-compact that didn't drive too well afterwards Lame

. Unfortunately, I was in the car when the "conversion" took place Lame

, so bear with me a little. But I love to hack, and CE is my favorite tool for debuggery (debauchery?) Razz

I *devastate* on game mods (I am a feared admin on Freelancer), but admittedly my hacks are pretty weak right now. I am at least clever enough to look for instructions adjacent to the one the debugger found. I try to examine the code block as best as I can, instead of just NOP'ing the initial "hit". I prefer to alter the instruction rather than just remove it.

Sorry, I'm running-on...Okay, back to code syntax and flow again for me. Thanks again.