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malis2007
How do I cheat?
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Joined: 31 Jul 2017
Posts: 1
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 Posted: Fri Aug 11, 2017 9:47 pm Post subject: need help understanding the carry flag.. |
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Hello there 
i have a problem understanding the carry flag :/
i added these lines to the SUB instruction in the CE's step 2 TUT
| Code: | pushad
pushfd
mov eax,2
add eax,1
popfd
popad |
after the add instruction, why is the carry flag being set? (CF=1)
>>image in attachment <<
and why is it cleared (CF=0) when i replaced this code:
with either 7,A or even F the carry flag is cleared? (CF=0)
e.g.
>> image in attachment <<
Thanks for reading, and your help inadvanced.. |
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OldCheatEngineUser
Whateven rank
 Reputation: 20
Joined: 01 Feb 2016
Posts: 1584
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| Posted: Fri Aug 11, 2017 10:12 pm Post subject: |
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| Quote: | Carry Flag
The rules for turning on the carry flag in binary/integer math are two:
The carry flag is set if the addition of two numbers causes a carry out of the most significant (leftmost) bits added. 1111 + 0001 = 0000
(carry flag is turned on)
The carry (borrow) flag is also set if the subtraction of two numbers requires a borrow into the most significant (leftmost) bits subtracted. 0000 - 0001 = 1111
(carry flag is turned on) Otherwise, the carry flag is turned off (zero).
0111 + 0001 = 1000 (carry flag is turned off [zero])
1000 - 0001 = 0111 (carry flag is turned off [zero])
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About Me;
I Use CE Since Version 1.X, And Still Learning How To Use It Well!
Jul 26, 2020
| STN wrote: | | i am a sweetheart. |
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FreeER
Grandmaster Cheater Supreme
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Joined: 09 Aug 2013
Posts: 1091
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| Posted: Sat Aug 12, 2017 7:32 am Post subject: |
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@OldCheatEngineUser the second image is 2 + 1, 00000010 + 00000001 = 00000011, at what point is that causing a carry out, or a borrow, from the most significant bit?
You can see the >> on the popfd so the add has been run but the flag restore has not.
Hello again @malis2007 I'm sure it's something that'll seem simple once it's pointed out but I'm not seeing it either lol |
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