Fib.asm

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.186 ;You may need to uncomment this to get some of the instructions working (e.g. shl, dest, count)
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data	segment											; data segment. Keyword db means define byte. You can also define word (dw)
		n		dw  5									;nth fib. number
		firstS 	db  'The Fibonacci number of order $'	;First part of output string
		secS	db	' is $'								;Second part of output string
		newL	db  0ah,'$'								;New line character
		temp	db	1 dup(?),'$'						;Used for output
data	ends

										; stack segment
stack1  segment	stack 		
		db	100 dup(?)      			; This is the stack of 100 bytes
stack1  ends


code    segment
        assume  cs:code, ds:data, ss:stack1

start: 
										;Perform initialization 
		mov ax, data					;Put the starting address of the data segment into the ax register (must do this first)
		mov ds, ax						;Put the starting address of the data segment into the ds register (where it belongs)
		
		mov ax, stack1					;Put the starting address of the stack into the ax register (must do this first)
		mov ss, ax						;Put the starting address of the stack segment into the ss register (where it belongs)
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;****************** Write Code Here ******************	
		
		mov cx, n			;Move n into cx (counter for the loop)
		
		mov bl, 0			;Initialize bl to 0 (used to store result)
		mov dl, 0			;Store current fib. # (i.e. 0 is the 0th fib. #)
		call pEvery			;Output Fibonacci number
		
		cmp cx, 0			;Check to see if cx is 0
		je fEnd				;Jump to end if cx == 0
		
		mov al, 0			;Initialize al to 0
		mov bl, 1			;Initialize bl to 1
		
		inc dl				;Increment dl to indicate the current fib. #
		
		
		dec cx				;Decrement cx for algorithm
		call pEvery			;Output Fibonacci numbers
		jz fEnd
				
loopS:						;Loop label

		add bl, al			;Add al and bl and store result in bl (nth fib. #)
		
		dec cx				;Decrement counter
		inc dl				;Increment dl to indicate current fib. #
		
		call pEvery			;Output Fibonacci number		
		
		cmp cx, 0			;Check if finished processing
		jg	loopS			;Continue while cx>0
		
fEnd:
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		mov ah, 4ch 		;Set up code to specify return to dos
        int 21h				;Interpt number 21 (Return control to dos prompt)
		
pEvery 	proc		
		push ax				;Back up ax
		push dx				;Back up dx
		
		mov temp, dl		;Put dl into memory for output
		add temp, 30h		;Convert dl into character			
		
		mov ah, 9			;Specify print string service routine
		
		lea dx, firstS		;Put the first part of output string into dx
		int 21h				;Request service from the OS
		
		lea dx, temp		;Put address of current number of fib. into dx
		int 21h				;Request service from the OS
		
		lea dx, secS		;Put the second part of output string into dx
		int 21h				;Request service from the OS
		
		mov temp, bl		;Put current fib. # into memory
		add temp, 30h		;Convert it to a character
		
		lea dx, temp		;Put address of current fib. number into dx
		int 21h				;Request service from the OS
		
		lea dx, newL		;Put address for new line string into dx
		int 21h				;Request service from the OS
		
		pop dx				;Restore dx
		pop ax				;Restore the value of ax

		ret
pEvery 	endp
;*****************************************************		

code    ends

end     start
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