Array in Hexadecimal in Assembly x86 MASM

Question

If: (I believe the registers are adjacent to one another...)

 A BYTE 0xB, 0d20, 0d10, 0d13, 0x0C
 B WORD 0d30, 0d40, 0d70, 0hB 
 D DWORD 0xB0, 0x200, 0x310, 0x400, 0x500, 0x600

Then:

What is [A+2]? The answer is 0d20 or 0x15
What is [B+2]? The answer is 40 or 0x28
What is [D+4]? Not sure
What is [D-10]? Not sure

I think those are the answers but I am not sure. Since a WORD is 1 BYTE, AND DWORD is 2 WORDS, then as a result when you are counting the array of [B+2] for example, you should be starting at 0d30, then 0d40 (count two WORD). And [A+2] is 0d20 because you are counting two bytes. What am I doing wrong?

So is it because: Taking into account that the first value of A,B, and D are offsets x86 is little endian... A = 0d10, count 2 more from there B...bytes (in decimal) = 30,0,40,0,70,0,11,0 B is 0d40, count 2 more bytes from that D...bytes (in hex) = 0x200, 0,0,0,...0,2,0,0,...0x10,3,0,0,...0,4,0,0,...0,5,0,0,...0,6,‌0,0 D is 0x200. Count 4 bytes from there. Count 10 bytes backwards from 0xb0. So wouldn't [D-10] be equal to 0x0C?

Also if I did [B-3], would it be 0d13? I was told it actually is between 0d10 and 0d13 such that it will be 0A0D and due to little endian will be 0D0A. Is that correct?

While the The M is for MicroSoft, the OS really has nothing to do with this problem. — candied_orange
– candied_orange, Commented Oct 16, 2016 at 4:31

John Wu · Accepted Answer · 2016-10-16 06:15:50Z

2

What is [A+2]? The answer is 0d20 or 0x15

Start at [A] (which is the same as [A+0]), go forward two bytes

A BYTE 0xB, 0d20, 0d10, 0d13, 0x0C
       ^0   ^1    ^2

Answer: 0d10

What is [B+2]? The answer is 40 or 0x28

A word is two bytes

Offsets are always in bytes. Therefore +2 = +2 bytes = +1 word

B WORD 0d30, 0d40, 0d70, 0hB 
   ^0    ^+2  <--bytes
   ^0    ^+1  <--words

Answer: 0d40

What is [D+4]? Not sure

Each dword is four bytes

Indexes are always in bytes, so +4 = +4 bytes = +1 dword

Start at [D] which is the same as [D+0]... more forward one

D DWORD 0xB0, 0x200, 0x310, 0x400, 0x500, 0x600 
        ^0    ^+1   <--dwords
        ^0    ^+4   <--bytes

Answer: 0x200

What is [D-10]? Not sure

Offsets are always in bytes

A dword contains four bytes

A word contains two bytes

A BYTE 0xB, 0d20, 0d10, 0d13, 0x0C
                        ^-10  ^-9
B WORD 0d30, 0d40, 0d70, 0hB 
       ^-8   ^-6   ^-4   ^-2
D DWORD 0xB0, 0x200, 0x310, 0x400, 0x500, 0x600 
        ^0

Answer: 0d13

answered Oct 16, 2016 at 6:15

John Wu

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jackson blackson Over a year ago

AMAZING!! THANK YOU

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