1                                  ; File: index1.asm
     2                                  ; 
     3                                  ; This program demonstrates the use of an indexed addressing mode
     4                                  ; to access array elements.
     5                                  ;
     6                                  ; This program has no I/O. Use the debugger to examine its effects.
     7                                  ;
     8                                  	SECTION	.data			; Data section
     9                                  
    10 00000000 000000000100000002-     arr:	dd 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ; ten 32-bit words
    11 00000009 000000030000000400-
    12 00000012 000005000000060000-
    13 0000001B 000700000008000000-
    14 00000024 09000000           
    15                                  base:	equ arr - 4
    16                                  
    17                                  	SECTION .text			; Code section.
    18                                  	global _start
    19 00000000 90                      _start: nop				; Entry point.
    20                                  
    21                                  	; Add 5 to each element of the array stored in arr. Simulate:
    22                                  	;
    23                                  	;  for (i = 0 ; i < 10 ; i++) {
    24                                  	;     arr[i] += 5 ;
    25                                  	;  }
    26                                  
    27 00000001 B900000000              	mov	ecx, 0			; ecx simulates i
    28 00000006 83F90A                  loop1:	cmp	ecx, 10			; i < 10 ?
    29 00000009 7D0E                    	jge	done1
    30 0000000B 81048D[00000000]05-     	add	[4*ecx+arr], dword 5	; arr[i] += 5
    31 00000013 000000             
    32 00000016 41                      	inc	ecx			; i++
    33 00000017 EBED                    	jmp	loop1
    34                                  done1:
    35                                  
    36                                  	; more idiomatic for an assembly language program
    37 00000019 B909000000              	mov	ecx, 9			; last array element's index
    38 0000001E 81048D[00000000]05-     loop2:  add	[4*ecx+arr], dword 5 	
    39 00000026 000000             
    40 00000029 49                      	dec	ecx
    41 0000002A 7DF2                    	jge	loop2			; again if ecx >= 0
    42                                  
    43                                  
    44                                  	; another way 
    45 0000002C BF[FCFFFFFF]            	mov	edi, base		; base computed at load time
    46 00000031 B90A000000              	mov	ecx, 10			; for(i=10 ; i>0 ; i--)
    47 00000036 81048F05000000          loop3:  add	[edi+4*ecx], dword 5 	
    48 0000003D E2F7                    	loop	loop3			; loop = dec ecx, jne
    49                                  
    50                                  alldone:
    51 0000003F BB00000000              	mov	ebx, 0			; exit code, 0=normal
    52 00000044 B801000000              	mov	eax, 1			; Exit.
    53 00000049 CD80                    	int	80H			; Call kernel.