231 Simple Arithmetic in Assembly

--D. Thiebaut (talk) 07:57, 23 September 2014 (EDT)

---

simpleAdd.asm

 
;;; -----------------------------------------------------
;;; simpleAdd.asm
;;; D. Thiebaut
;;; Simple program that adds 2 integers together.
;;;
;;; To assemble, link and run:
;;; nasm -f elf 231Lib.asm
;;; nasm -f elf simpleAdd.asm
;;; ld -melf_i386 simpleAdd.o 231Lib.o -o simpleAdd
;;; ./simpleAdd
;;; -----------------------------------------------------

;;; extern functions that will be linked to this program
;;; contained in 231Lib.asm

extern  _printDec
extern  _printString
extern  _println
extern  _getInput
        
;;; -----------------------------------------------------
;;; data section
;;; -----------------------------------------------------
        section .data
a       dd      3
b       dd      5
c       dd      0       
prompt  db      "> "
        
;;; -----------------------------------------------------
;;; code section
;;; -----------------------------------------------------
        section .text
        global _start
_start:

;;; compute c = a + b;
        mov             eax, dword[a]
        add             eax, dword[b]
        mov             dword[c], eax
        
;;; print c on the screen, as decimal number, then go to next line.

        mov             eax, dword[c]
        call            _printDec
        call            _println

;;; ; exit
        mov             ebx, 0
        mov             eax, 1
        int             0x80

simpleAdd2.asm

• This version prompts the user to input both a, and b.

;;; -----------------------------------------------------
;;; simpleAdd2.asm
;;; D. Thiebaut
;;; Simple program that prompts the user for 2 numbers and
;;; computes their sum.  The result is printed on the screen.
;;;
;;; To assemble, link and run:
;;; nasm -f elf 231Lib.asm
;;; nasm -f elf simpleAdd2.asm
;;; ld -melf_i386 simpleAdd2.o 231Lib.o -o simpleAdd2
;;; ./simpleAdd2
;;; -----------------------------------------------------

;;; extern functions that will be linked to this program
;;; contained in 231Lib.asm

extern  _printDec
extern  _printString
extern  _println
extern  _getInput
        
;;; -----------------------------------------------------
;;; data section
;;; -----------------------------------------------------
        section .data
a       dd      3
b       dd      5
c       dd      0       
prompt  db      "> "
        
;;; -----------------------------------------------------
;;; code section
;;; -----------------------------------------------------
        section .text
        global _start
_start:

;;; get 32-bit int a from user
        mov             ecx, prompt             ; display "> "
        mov             edx, 2
        call            _printString
        
        call            _getInput               ; get int in eax
        mov             dword[a], eax           ; store in a


;;; get 32-bit int b from user
        mov             ecx, prompt             ; display "> "
        mov             edx, 2
        call            _printString
        
        call            _getInput               ; get int in eax
        mov             dword[b], eax           ; store in b


;;; compute c = a + b;
        mov             eax, dword[a]
        add             eax, dword[b]
        mov             dword[c], eax
        
;;; print c on the screen, as decimal number, then go to next line.

        mov             eax, dword[c]
        call            _printDec
        call            _println

;;; ; exit
        mov             ebx, 0
        mov             eax, 1
        int             0x80