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Ali.Z



Joined: 08 Jan 2018
Posts: 734
Ali.Z 11 Oct 2019, 15:56
Code:
somewhere:
xor ecx,ecx
loop somewhere    


intel clearly said "decrement counter and then check if counter is 0" so that means if ecx is 0 already it should loop.
and thats fine, and we all know this.

however in intel's code samples, representing x86 asm in C\CPP intel represented the loop instruction in a wrong way.
saying that it first check if the counter is 0 and if its not it takes the loop, so thats probably a mistake made by intel.

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Post 11 Oct 2019, 15:56
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 20453
Location: In your JS exploiting you and your system
revolution 11 Oct 2019, 16:13
One way to be sure is to test it and see which of the two descriptions actually happens.
Post 11 Oct 2019, 16:13
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DimonSoft



Joined: 03 Mar 2010
Posts: 1228
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DimonSoft 11 Oct 2019, 19:50
First one.

I wouldn’t tell C/C++ examples serious while talking about instructions. After all, they’re not documentation and are rarely written by people who actually spen much time using the instructions directly.
Post 11 Oct 2019, 19:50
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Ali.Z



Joined: 08 Jan 2018
Posts: 734
Ali.Z 12 Oct 2019, 06:05
i know its the first one, im just saying there are some mistakes.

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Post 12 Oct 2019, 06:05
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fpissarra



Joined: 10 Apr 2019
Posts: 64
fpissarra 12 Oct 2019, 13:24
Where are you getting the Intel C/C++ equivalent code? It is not in Intel 64 and IA-32 Architectures Software Development Manual Vol 2. There, the behavior of the instruction is well defined in pseudo-code.
Post 12 Oct 2019, 13:24
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