Get index of array element in Assembly

Question

Let me start this by saying that I do know I am not supposed to be brute forcing the program, but I am at a bit of an impasse, the purpose is to use the elements of one array to basically "sort" the elements of another array.

Given:

start = 1

chars: H,A,C,E,B,D,F,G links: 0,4,5,6,2,3,7,0

So you'd start at the first element, A, which is also the number 4 in the links array, which points to the letter B in the chars array, and so on and so forth. The characters are stored in a new array in alphabetical order, where I am having trouble in is getting the index number of the chars array after every step, maybe the code will show a bit more where I am having trouble

   INCLUDE Irvine32.inc

   start = 1

   .data

    chars BYTE 'H','A','C','E','B','D','F','G'
links DWORD 0,4,5,6,2,3,7,0
array BYTE 0,0,0,0,0,0,0,0

.code 
main PROC
mov al, chars +1
mov array, al
mov esi, start          ; moves the start location into the esi register
mov eax, [links + 4]    ; moves the second element of the array into eax
mov dl, chars[eax]      ; moves the character element of the array chars into dl
mov array[esi], dl      ; moves the character into the array
inc esi
mov eax, [links + 16]
mov dl, chars[eax]
mov array[esi], dl
inc esi
mov eax, [links + 8]
mov dl, chars[eax]
mov array[esi], dl
inc esi
mov eax, [links + 20]
mov dl, chars[eax]
mov array[esi], dl
inc esi
mov eax, [links + 12]
mov dl, chars[eax]
mov array[esi], dl
inc esi
mov eax, [links + 24]
mov dl, chars[eax]
mov array[esi], dl
inc esi
mov eax, [links + 28]
mov dl, chars[eax]
mov array[esi], dl
inc esi

    main ENDP
    END main

So I think if I just knew how to get the index of the array element after the "links" array points to it I think I could put it into a loop, I just need to know how to do that.

Just store the offset into a register. Also, use the Indexed Addressing Mode. — cadaniluk
– cadaniluk, Commented Oct 22, 2015 at 9:39

Fifoernik · Accepted Answer · 2015-10-22 10:21:05Z

2

  mov al, chars +1
  mov array, al
  mov esi, start          ; moves the start location into the esi register
  mov ebx, offset links
Again:
  mov eax, [ebx + esi*4]  ; moves the next element of the array into eax
  mov dl, chars[eax]      ; moves the character element of the array chars into dl
  mov array[esi], dl      ; moves the character into the array
  inc esi

Repeat this code the required number of times by testing the ESI register.

You could improve this code by starting at 0 in stead of 1. It would eliminate the 2 lines at the top. It would need modifying the definition of links.

links DWORD 1,4,5,6,2,3,7,0

answered Oct 22, 2015 at 10:21

Fifoernik

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