RosettaCodeData/Task/Fibonacci-sequence/8080-Assembly/fibonacci-sequence-2.8080

	;-------------------------------------------------------
	; useful equates
	;-------------------------------------------------------
bdos	equ 	5	; BDOS entry
cr	equ 	13	; ASCII carriage return
lf	equ 	10	; ASCII line feed
space	equ	32	; ASCII space char
conout	equ 	2	; BDOS console output function
putstr	equ	9	; BDOS print string function
nterms	equ	20	; number of terms (max=24) to display
	;-------------------------------------------------------
	; main code begins here
	;-------------------------------------------------------
	org	100h
	lxi	h,0		; save CP/M's stack
	dad	sp
	shld	oldstk
	lxi	sp,stack	; set our own stack
	lxi	d,signon	; print signon message
	mvi	c,putstr
	call	bdos
	mvi 	a,0		; start with Fib(0)
mloop:	push	a		; save our count	
	call 	fib
	call	putdec
	mvi	a,space		; separate the numbers
	call	putchr
	pop	a		; get our count back
	inr	a		; increment it
	cpi	nterms+1	; have we reached our limit?
	jnz	mloop		; no, keep going
	lhld	oldstk		; all done; get CP/M's stack back
	sphl			; restore it
	ret			; back to command processor
	;-------------------------------------------------------
	;  calculate nth Fibonacci number (max n = 24)
	;  entry: A = n
	;  exit:  HL = Fib(n)
	;-------------------------------------------------------
fib:	mov 	c,a	; C holds n
	lxi 	d,0	; DE holds Fib(n-2)
	lxi 	h,1	; HL holds Fib(n-1)
	ana	a	; Fib(0) is a special case
	jnz	fib2	; n > 0 so calculate normally
	xchg		; otherwise return with HL=0
	ret
fib2:	dcr	c
	jz	fib3	; we're done
	push 	h	; save Fib(n-1)
	dad 	d	; HL = Fib(n), soon to be Fib(n-1)
	pop 	d	; DE = old F(n-1), now Fib(n-2)
	jmp 	fib2	; ready for next pass
fib3:	ret
	;-------------------------------------------------------
	; console output of char in A register
	;-------------------------------------------------------
putchr:	push	h
	push	d
	push	b
	mov	e,a
	mvi	c,conout
	call	bdos
	pop	b
	pop	d
	pop	h
	ret
	;---------------------------------------------------------
	; Output decimal number to console
	; HL holds 16-bit unsigned binary number to print
	;---------------------------------------------------------
putdec: push	b
	push	d
	push	h
	lxi	b,-10
	lxi	d,-1
putdec2:
	dad	b
	inx	d
	jc	putdec2
	lxi	b,10
	dad	b
	xchg
	mov	a,h
	ora	l
	cnz	putdec		; recursive call
	mov	a,e
	adi	'0'
	call	putchr
	pop	h
	pop	d
	pop	b
	ret
	;-------------------------------------------------------
	; data area
	;-------------------------------------------------------
signon: db	'Fibonacci number sequence:',cr,lf,'$'
oldstk:	dw	0
stack	equ	$+128		; 64-level stack
	;
	end