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Rudo
Advanced Cheater
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Joined: 27 Jun 2015
Posts: 80
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 Posted: Tue Jun 30, 2015 9:23 am Post subject: How to copy a float value of an address to another address ? |
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Say I have [edi+0000015C] in float
I want to copy the value of [edi+0000015C] to [edi+00000160], which is float too. How do I do this?
I have written this code but it doesn't work, when I activate the script, the value in [edi+00000160] becomes a very wierd ...
| Code: | originalcode:
push ebx
mov ebx,[edi+0000015C]
cmp [edi+00000160],ebx
je exit
mov [edi+00000160],ebx
pop ebx
jmp exit
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Can you explain what I did wrongly?
Does my script work if those are 4 bytes addresses?
If you give me a correct script for float, do I still have to rewrite if the address is 1 byte, 2 bytes, double, ect. ?
One more thing: It seems like when I activate the script, my value change and that is it. No more. How do I write a script that it keep copying the value in [edi+0000015C] to [edi+00000160] as I play the game?
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Dark Byte
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| Posted: Tue Jun 30, 2015 9:31 am Post subject: |
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weird behaviour is weird itself, the game should have crashed because if the value at edi+160 matches ebx the pop ebx instruction is skipped causing severe stack corruption
so first off remove that compare and je
also, i think you may be skipping the original code, so that also means it's skipped for the other things this code accesses
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Rudo
Advanced Cheater
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Joined: 27 Jun 2015
Posts: 80
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| Posted: Tue Jun 30, 2015 9:51 am Post subject: |
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I have learnt Assembly for just 2 days and barely know anything about it so I think I will need a lot of help ...
EDIT: Nevermind, I tried to removed cmp and je then rewrite all the script and it works fine. Thank you.
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atom0s
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| Posted: Tue Jun 30, 2015 11:09 am Post subject: |
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| Rudo-kun wrote: | | I have learnt Assembly for just 2 days and barely know anything about it so I think I will need a lot of help ... |
Like Dark Byte mentioned, you are killing the stack with the original script you posted in the first post. This is where your issue lies:
| Code: |
originalcode:
push ebx
mov ebx,[edi+0000015C]
cmp [edi+00000160],ebx
je exit
mov [edi+00000160],ebx
pop ebx <--- This is never called if you jump which is leaving data on the stack that should not be there!
jmp exit
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Instead, you would need to have that pop before you are jumping to exit to ensure the stack is cleared from the data that you have pushed onto it.
Given that you are just comparing if its equal and not moving if it is, there is really no need to do that you can just move it into the address no matter what since the results will be the same. For example, the clock cycles used for what you are doing would be something like:
| Code: |
push ebx <-- 3
mov ebx,[edi+0000015C] <-- 2
cmp [edi+00000160],ebx <-- 1
je exit <-- ? (Undefined latency due to branching etc that is taken into consideration.)
mov [edi+00000160],ebx <-- 3
pop ebx <-- 2
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So you are adding an unneeded 1+(n) clock cycles based on the jumps evaluated clock cycle count based on where its jumping to. Instead just cutting it down to the base push/pop and moves will give the same results, with less clock cycles:
| Code: |
push ebx <-- 3
mov ebx,[edi+0000015C] <-- 2
mov [edi+00000160],ebx <-- 3
pop ebx <-- 2
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Conditional jumps have a varying number of clock cycles based on what is being done. For example, JE typically uses around 16 clock cycles on an 8086 processor if the jump is taken, while when no jump is taken it uses around 4 clock cycles. So with that, it is best to code jumps so that the non-jump condition is the one executed the most for the least clock cycles.
Note that the clock cycle information in this post will vary based on the processor in use while executing this code. The data I used is from the Core i7 instruction information based on the [code named] 'Nehalem' processor series.
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Rudo
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Joined: 27 Jun 2015
Posts: 80
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| Posted: Tue Jun 30, 2015 11:55 am Post subject: |
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| Thank you for the lesson. I will learn more about Assembly so these mistakes won't happen again.
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