Question

Write an assembly program that rearrange the values in the following array as 40, 30, 20, 10:

.data byte1 BYTE 10, 20, 30, 40

Save the original four byte data into eax, and the rearranged data into ebx, from the least significant bit to the most significant bit. Insert a call DumpRegs statement to display the register values.

Answer 1

instruction    source offset     result
mov bx,[bx]     1000h             1BACh
mov cx,[si]     2000h             20FEh
mov bx,[ax]     illegal source register
add [si],[di]   illegal memory-memory add
inc [di]        3000h             031Eh

Processing Arrays using Register-Indirect Mode

• Sum in ax the 10-element word array W

W   dw   10,20,30,40,50,60,70,80,90,10

xor ax,ax     ; ax holds sum
lea si,W      ; si points to array W
mov cx,10     ; cx has number of elements

addnos:

add ax,[si]   ; sum = sum + element
add si,2      ; move pointer to the next element
loop addnos    ; loop until done

1. .code
2. main PROC
3. mov ax,8000h ;ax = 8000h
4. mov bx,2000h ;bx = 2000h
5. mov cx,3000h ;cx = 3000h
6. sub ax,bx ;subtract bx from ax, ax = 6000h
7. sub ax,cx ;subtract cx from ax, ax = 3000h
8. sub cx,bx ;subtract bx from cx, cx = 1000h
9. call DumpRegs ;display registers
10. exit ;halt program
11. main ENDP ;end procedure
12. END main ;end program