CODEWITHSUNDEEP
c++assemblyx86zero-extension
1ntgr
1ntgr

Reputation: 126

Translate assembly instructions to c++

I am having trouble translating the below assembly in to c++

MOVZX EAX, DX

Where EDX is a 32bit register. I need to get the lowest 16 bits(DX).

I've tried the following:

unsigned edx = 0x123ABCDE;
unsigned dx = (edx>>16) & 0xff;

I expect to get an the value of BCDE stored in dx, but it's gone a bit wrong.

Any help would be much appreciated.

Upvotes: 1

Views: 101

Answers (1)

Thomas Matthews
Thomas Matthews

Reputation: 57729

Let's analyze your code step by step.
unsigned edx = 0x123ABCDE;
Nothing unusual.

Let's break up the next statement according to order of evaluation.
(edx >> 16) -- right shift by 16 bits.
This is right shifting by 2 bytes or 4 hex digits.
Answer should be 0x123A.

Now, let's keep the right most 8 bits (ANDing with 0xFF):
0x123A & 0xFF == 0x3A

The result should be 0x3A in the variable dx.

Upvotes: 2

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