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how does 16 bit register works ?


kb432

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Posted

what is moving something to cl or ax or dl ? 

what does it mean ? i know it's 16 bit register. Can anyone give me an example so i understand better ? 

Thanks 

Posted
EAX is a 32bit register, but you can still access the last 16 bits (compatibility etc)

EAX is the full 32-bit value
AX is the lower 16-bits
AL is the lower 8 bits
AH is the bits 8 through 15 (zero-based)

e.g.

EAX   BADC0DE5

AX               0DE5

AH               0D

AL                   E5

Posted (edited)

PS as loki stated above just a addition if its RAX its 64bit :)

AX - x means extended

H means higher and L means lower

Edited by Jasi2169
Posted

Watch out with RAX, it doesn't work in the same way as subregisters for EAX. If you do "mov eax,12345678" in x64, you will get "RAX = 12345678 & 0xFFFFFFFF", effectively clearing the upper part of RAX.

Posted
On 9/24/2016 at 7:45 PM, CodeCracker said:

what is i want to access "BADC" ?

Posted (edited)

CodeCracker never said that! :D:P

SHR r/m8 = Unsigned divide r/m8 by 2, 1 time.
If EAX = BADC0DE5 and you want BADC
you divide EAX to 2^16 = 65536 ( SHR is divide by power of two).

Edited by CodeCracker
Posted

If you want BACD use the instruction shr eax, 0x10 or 0xBADC0DE5 >> 16

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