* REENTRANT MULTIPLICATION
*  MULTIPLIES TWO 8 BIT UNSIGNED NUMBERS GIVING
*  A 16 BIT UNSIGNED PRODUCT
*  A * B = A,B
*
	ORG	$0
TEST	LDS	#STACK
	LDA A	#10
	LDA B	#20
	JSR	MPY8	;CALL MULTIPLY SUBROUTINE
	JMP	*
	
MPY8	PSH A		;MULTIPLICAND TO STACK
	LDA A	#8
	PSH A		;COUNT TO STACK
	TSX
	CLR A
	ROR B
M3	BCC	M4	;DO NOT ADD
	ADD A	1,X	;ADD MULTIPLICAND
M4	ROR A
	ROR B
	DEC	0,X	;DECREMENT COUNT
	BNE	M3

	INS		;RESTORE STACK
	INS

	RTS		;SUBROUTINE RETURN

	RMB	20	;TEMP STORAGE FOR STACK
STACK	RMB	1	;START OF STACK (WHEN EMPTY)
	END