51 lines
1.5 KiB
NASM
51 lines
1.5 KiB
NASM
bits 32 ; assembling for the 32 bits architecture
|
|
|
|
; declare the EntryPoint (a label defining the very first instruction of the program)
|
|
global start
|
|
|
|
; declare external functions needed by our program
|
|
extern exit ; tell nasm that exit exists even if we won't be defining it
|
|
import exit msvcrt.dll ; exit is a function that ends the calling process. It is defined in msvcrt.dll
|
|
; msvcrt.dll contains exit, printf and all the other important C-runtime specific functions
|
|
|
|
; our data is declared here (the variables needed by our program)
|
|
|
|
|
|
;Given a byte string S of length l, obtain the string D of length l-1 as D(i) = S(i) * S(i+1) (each element of D is the product of two consecutive elements of S).
|
|
|
|
|
|
segment data use32 class=data
|
|
; ...
|
|
S db 1,2,3,4
|
|
l equ $-S
|
|
D resw l-1
|
|
|
|
; our code starts here
|
|
segment code use32 class=code
|
|
start:
|
|
; ...
|
|
; mov ECX,0
|
|
; jmp_label:
|
|
; mov AL,[S+ECX]
|
|
; mov BL,[S+ECX+1]
|
|
; imul BL
|
|
; mov [D+2*ECX],AX
|
|
; inc ECX
|
|
; cmp ECX,l-1
|
|
; jb jmp_label
|
|
|
|
mov ECX,l
|
|
mov ESI,0
|
|
jmp_label:
|
|
mov AL,[S+ESI]
|
|
mov BL,[S+ESI+1]
|
|
imul BL
|
|
mov [D+2*ESI],AX
|
|
inc ESI
|
|
loop jmp_label
|
|
|
|
|
|
; exit(0)
|
|
push dword 0 ; push the parameter for exit onto the stack
|
|
call [exit] ; call exit to terminate the program
|