Slide 2.c: An assembly program

An Assembly Program

Assembly languages are used when speed is essential or when an operation is needed that is not possible in a high-level language. The following Microsoft MASM assembly program generates and prints up to N, entered by a user, Fibonacci numbers, where

Irvine32.inc is an inclusion file provided by Kip Irvine.
EAX, EBX, ECX, and EDX are 32-bit general-purpose registers.
The procedure WriteString prints the string whose beginning address is at EDX.
The procedure ReadInt reads an integer from the screen and puts the result at EAX.
The procedure WriteDec prints a nonnegative integer at EAX on the screen.
The loop command loop target transfers the execution sequence to target, ECX times.

Fibonacci.asm

 TITLE Fibonacci Numbers              (Fibonacci.asm)

 INCLUDE Irvine32.inc

 .data
 prompt1  BYTE   "Find the first N values of the Fibonacci numbers.", 0Dh, 0Ah
          BYTE   0Dh, 0Ah, "Enter the value of N (positive integer):  ", 0
 prompt2  BYTE   "  ", 0
 n        DWORD  ?

 .code
 main PROC
     call  Clrscr                ; Clears the screen.
     mov   edx, OFFSET prompt1
     call  WriteString           ; Prints the prompt 1.
     call  ReadInt               ; Reads the N.
     mov   n, eax
     call  Crlf                  ; Prints a newline.

     mov   ecx, n                ; Computes and prints N Fibonacci numbers.
     mov   eax, 1                ; Initializes Fib(1) = 1.
                                 ; eax = 1, 1, 2, 3, 5, 8, 13, ...
     mov   ebx, 0                ; Fib(2) = Fib(1) + 0.
 
 L1: add   eax, ebx              ; Generates the next Fibonacci number.
     call  WriteDec              ; Prints the number. 
     mov   edx, OFFSET prompt2   
     call  WriteString           ; Prints spaces.
            ; Sets up the sequence.
     loop  L1

     call  Crlf
     call  Crlf
     exit
 main ENDP
 END main