Counting Characters

Three versions of a program to count the number of characters in a character string. 
Exercise:  Work through each of the versions to see what they do and write written descriptions
flow charts.   

Version 1

data	equ	$6000
program equ	$4000

	org	data

start	ds.l	1
length	ds.w	1

cr	equ	$0d

	org program

	movea.l	start, a0
	moveq	#0, d0

loop	cmpi.b	#cr, (a0)+
	beq.s	done
	addq.w	#1, d0
	bra loop

done	move.w	d0, length

rts
end

Version 2

data	equ	$6000
program equ	$4000

	org	data

start	ds.l	1
length	ds.w	1

cr	equ	$0d

	org program

	movea.l	start, a0
	moveq	#-1, d0
	moveq	#cr, d1
loop	addq.w	#1, d0

	cmp.b	d1, (a0)+

	bne	loop

	move.w	d0, length

	rts
	end

Version 3

data	equ	$6000
program equ	$4000

org	data

start	ds.l	1
length	ds.w	1

cr	equ	$0d

	org 	program

	movea.l	start, a0
	moveq	#256-1, d2
	move.w	d2, d0
	moveq	#cr, d1

loop	cmp.b	d1, (a0)+
 	dbeq	d0, loop
	sub.w	d0, d2
	move.w	d2, length

	rts
	end

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