Question

This is Assembly Language...please i want you to give proper documentation or comment of every code you write, so i can understand your code. Thank you!

** 2. Exchanging Pairs of Array Values Write a program with a loop and indexed addressing that exchanges every pair of values in an array with an even number of elements. Therefore, item i will exchange with item i+1, and item i+2 will exchange with item i+3, and so on.

Answer 1

.386
.model flat,stdcall
.stack 4096
ExitProcess proto,dwExitCode:dword
.data
array dword 1,2,3,4,5,6,7,8 #array of elements
.code
main proc
mov esi, OFFSET array #move the all index values to the esi register
mov ecx, LENGTHOF array -1 #move the lenght of the array to the ecx register

myLoop: #loop start

MOV eax,[esi] #move the index of array value to the eax
XCHG eax,[esi+4]   #exchanging the two value pairs by adding bytes 4 then the address will be change
MOV [esi],eax #swap the value pairs

add esi, TYPE array #first swapped value add to the array
add esi, TYPE array # second swapped value add to the array

loop myLoop # iterate loop

invoke ExitProcess,0 # exit process
main endp
end main #end of the program

another method simply understands:

dwarray dword 0,2,5,9,10,12
.code
main proc
mov ebx, OFFSET dwarray
mov ecx, 3                    # THE ARRAY CONTAINS 6 ELEMENTS, BUT THEY ARE PROCESSED
                                   IN PAIRS, SO THE LOOP SHOULD REPEAT HALF 6 (3).
L1: ;cmp ebx, ecx            #UNNECESSARY?
mov eax, [ebx]
mov edx, [ebx+4]              #THE NEXT ELEMENT IS 4 BYTES AWAY.
mov [ebx+4], eax              #AGAIN, THE NEXT ELEMENT IS 4 BYTES.
mov [ebx], edx
add ebx, 8                    #INCREASE BY 8 (THE SIZE OF 2 ELEMENTS PROCESSED).
loop L1