rec			START	0
			JSUB	stackinit

mainloop	JSUB	readnum
			COMP	#0		.if 0 halt
			JEQ		halt
			JSUB	fac
			JSUB	printnum
			J		mainloop

readnum		STL		readret
			LDA		#0
			STA		currentnum
readchar	RD		devFA
			COMP	#10		.stop reading if newline
			JEQ		endread
			COMP	#48		.stop reading if 0
			JEQ		endread
			SUB		#48
			STA		temp
			LDA		currentnum
			MUL		#10
			ADD		temp
			STA		currentnum
			J		readchar
endread		LDA		currentnum
			LDL		readret
			RSUB

ending		LDA		temp
			JSUB	printnum
			J		mainloop

printnum	STL		printret
			STA		num
			LDA		#0
			STA		digitcnt
divloop		LDA		num
			COMP	#0
			JEQ		checkzero
			DIV		#10
			STA		quotient
			MUL		#10
			STA		saveA
			LDA		num
			SUB		saveA
			ADD		#48		.convert to ascii number
			STA		@stkptr
			JSUB	push
			LDA		digitcnt
			ADD		#1
			STA		digitcnt
			LDA		quotient
			STA		num
			J		divloop
checkzero	LDA		digitcnt
			COMP	#0
			JGT		printloop
			LDA		#48
			WD		devAA
			LDL		printret
			RSUB
printloop	LDA		digitcnt
			COMP	#0
			JEQ		printdone
			LDB		stkptr
			COMPR	X, B	.stop print if stack empty
			JEQ		printdone
			JSUB	pop
			WD		devAA
			LDA		digitcnt
			SUB		#1
			STA		digitcnt
			J		printloop
printdone	LDL		printret
			LDA		#0x0A	.print newline
			WD		devAA	
			RSUB	

halt		J		halt

fac			COMP	#1		.base case
			JGT		facrecur
			LDA		#1
			RSUB

							.only works for < 10 (24 bit registers)
facrecur	JSUB	push	.recursive case
			SUB		#1
			JSUB	fac
			STA		temp
			STL		lastJ	.save jump register
			LDB		stkptr
			COMPR	X, B	.exit if stack empty
			JEQ		ending
			JSUB	pop
			MUL		temp
			LDL		lastJ
			RSUB			

push		STA		temp
			STA		@stkptr
			LDA		stkptr
			ADD 	#3
			STA		stkptr
			LDA		temp
			RSUB

pop			STA		temp
			LDA		stkptr
			SUB		#3
			STA		stkptr
			LDA		@stkptr
			RSUB

stackinit	STA		temp
			LDA		#stack
			STA		stkptr
			LDX		stkptr
			LDA		temp
			RSUB

stkptr		RESW	1
temp		RESW	1
lastJ		RESW	1
printret	RESW	1
readret		RESW	1
currentnum	RESW	1
num			RESW	1
quotient	RESW	1
saveA		RESW	1
digitcnt	RESW	1
stack		RESW	50
devFA		BYTE	X'FA'
devAA		BYTE	X'AA'
			END		rec