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rc



Joined: 03 Nov 2019
Posts: 38
Location: Germany
rc
Hello,

can somebody tell me why this produces an integer overflow when i do the division?

Code:
format PE
entry main
section '.code' code readable executable

main:
        int3
        mov eax, 4
        mov ecx, 2
        div ecx
        push eax      


4 is divided by 2, that shouldn't be a problem? Or am i missing something?
Post 16 Mar 2020, 20:46
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Feryno



Joined: 23 Mar 2005
Posts: 454
Location: Czech republic, Slovak republic
Feryno
but what is the input value in edx ?
if input edx 2 or more the result cannot fit into 32 bit register
try this:
Code:
mov eax,4
xor edx,edx    
Post 16 Mar 2020, 20:54
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rc



Joined: 03 Nov 2019
Posts: 38
Location: Germany
rc
Oh.. i guess i missunderstood div... ?
Code:
mov ecx, 2
div ecx    

So "div ecx" in my case divides whatever is in edx by 2?
I thought div ecx divides whatever is in eax by ecx in this case. And the result gets stored back into eax.

[EDIT]

Oh now i understand. div always divides the 64 bits value accross EDX:EAX by a value. Didn't know that. Thank you!
Post 16 Mar 2020, 21:01
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Tomasz Grysztar



Joined: 16 Jun 2003
Posts: 7756
Location: Kraków, Poland
Tomasz Grysztar
Well, it is definitely unfortunate that I have still not recorded part 10 of my video tutorial, which I planned to be about MUL/DIV. My fault, but I had to postpone continuation of this series for various unrelated reasons.
Post 17 Mar 2020, 17:02
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rc



Joined: 03 Nov 2019
Posts: 38
Location: Germany
rc
Tomasz Grysztar wrote:
Well, it is definitely unfortunate that I have still not recorded part 10 of my video tutorial, which I planned to be about MUL/DIV. My fault, but I had to postpone continuation of this series for various unrelated reasons.


@Tomasz Grysztar:
Well, we all have stuff to do besides our hobbies Smile.
I'm following your tutorial series since the beginning and hope you will find the time to continue soon. And i hope this series is going to be a really long series Smile. They are really helpful. Thanks for taking the time to teach the ones that are new to f/asm.
Post 17 Mar 2020, 18:53
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