lecture6-2, Assembly

lecture6-2

;File: index2.asm
;
;This program demonstrates the use of an indexed addressing mode
;to access array elements
;
;This program has no I/O. Use the debugger to examine its effects
;
;nasm -felf64 -g index2.asm -o index2.o
;ld -o index2 index2.o
;

section .data
        ;simulates a 2-dim array
twodim:
row1:   dd 00,01,02,03,04,05,06,07,08,09
row2:   dd 10,11,12,13,14,15,16,17,18,19
        dd 20,21,22,23,24,25,26,27,28,29
        dd 30,31,32,33,34,35,36,37,38,39
        dd 40,41,42,43,44,45,46,47,48,49
        dd 50,51,52,53,54,55,56,57,58,59
        dd 60,61,62,63,64,65,66,67,68,69
        dd 70,71,72,73,74,75,76,77,78,79
        dd 80,81,82,83,84,85,86,87,88,89
        dd 90,91,92,93,94,95,96,97,98,99
rowlen: equ row2-row1

section .text
global _start

_start:
        ;Add 5 to each element of the array stored in arr
        ;Simulate
        ;
        ; for (i=0; i<10 i++) {
        ;   twodim[i][7] += 5;
        ; }

init:   mov rcx,0                       ;rcx simulates i
        mov rax,4
        mov rdx,6
        mul rdx                         ; offset of twodim[0][7] rax = rax * rdx
        jc alldone                      ; if cf=1 (too big)

loop1:  cmp rcx,10                      ; i<10
        jge done1
        add [rax+twodim], dword 5       ; twodim[i][7] += 5
        inc rcx                         ; i++
        add rax,rowlen
        jmp loop1
done1:

alldone:
        mov rax,60
        xor rdi,rdi
        syscall


run \| edit \| history \| help	0