;; This section is for defining constants, such as filenames or buffer sizes,
;; It includes the initialized variables
	
section .data
miles	DW	180
gallons	DW	6
mpg	DW	0
nrDays	DB	141
weeks	DB	0
days	DB	0
string1	DB	'mpg is %d', 10,0
string2 DB      'Second try is %d', 10, 0
string3 DB	'The number of hours in a week is %d', 10, 0
bigNum	DD	0


;; This section is where you declare your uninitialized variables.
section .bss

;; This is where the actual assembly code is written. 
section .text
    global main                       ;must be declared for linker (ld)
extern	printf
main:                                 ;tell linker entry point

;; put your code here

	mov  	ax, word [miles]
	cwd             	;ax is assumed
	idiv 	word [gallons]	;ax is assumed
	mov  	[mpg], ax

	mov  	eax, 0
        mov  	ax, [mpg]
	push 	eax
	push 	string1
	call 	printf
	add	esp, 8

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; DANGER: What happens with the registers when you call
;;         another function?  
;;
;;	   Let's look at it.  Repeat the pushes and call
;;         printf again!
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

	push 	eax
	push 	string2
	call 	printf
	add 	esp, 8
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; Something changed ax!
;;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

	mov 	al, [nrDays]
	sub 	ah, ah      ;don't sign extend because that 
	                ;  would change the value
	mov 	bl, 7
	div 	bl          ;can't use a constant here!
	mov 	[weeks], al
	mov 	[days], ah    ;the remainder is the portion 

;
; One more example, this time with multiplication of a unsigned number
;
	mov	ax, 24	; there are 24 hours in a day
	mov	bx, 7	; How many hours in a week?
	mul	bx	; Calculate the answer
	push	eax
	push	string3
	call	printf
	add	esp, 8

;; The final part of the program must be a call to the operating system to exit
;;; the program.
        mov     ebx,0   ;successful termination of program
        mov     eax,1   ;system call number (sys_exit)
        int     0x80    ;call kernel

;; Notice the file just ends.

©2004, Gary L. Burt