using cmp with array. how to compare array elements in 8086

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how do you compare array elements?
lets say i have a variable named row and its value is 45
then an arr db 42,41

cmp row, arr[0] or cmp row, [arr]

both doesnt seem to work. or do i have to move the contents to a variable?? then use cmp?

Posted 7-Mar-15 6:08am

Reuben Cabrera

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Frankie-C · Answer 1 · 2015-03-07T07:13:00

Solution 1

You have to use a register as index to move in the array:

mov si, arr  ;register si points to base array
xor bx,bx    ;BX=0
mov al, BYTE PTR[ROW]
cmp al, BYTE PTR[SI+BX]  ;make comparison, address is SI(=arr)+BX(=index)
je  IsEqual  ;Match

For more info's you can see this[^].

Posted 7-Mar-15 7:13am

Frankie-C

Updated 7-Mar-15 7:15am

v2

Comments

Sergey Alexandrovich Kryukov 7-Mar-15 13:50pm

Looks correct at first glance, a 5. Did you validate it? It's a luck that this simple code is possible in the protected mode under modern OS. :-)
—SA

Frankie-C 7-Mar-15 15:49pm

Yes, it works, but is 8086 pure 16 bits code.
You cannot compile it under a 32 bits OS because of the pointers size.
To use it under 32 bits OS you have to change pointers size:

mov esi, arr ;register si points to base array
xor bx,bx ;BX=0
mov al, BYTE PTR[ROW]
cmp al, BYTE PTR[ESI+BX] ;make comparison, address is SI(=arr)+BX(=index)
je IsEqual ;Match

For 64 bits OS:

mov rsi, arr ;register si points to base array
xor bx,bx ;BX=0
mov al, BYTE PTR[ROW]
cmp al, BYTE PTR[RSI+BX] ;make comparison, address is RSI(=arr)+BX(=index)
je IsEqual ;Match

Thanks for the 5...