;; Do not try to read this code....
	.ORIG	x5000
L8MAIN	LEA	R0,MSG1
	PUTS
	LD	R5,MASC0	; R5 = -'0'
	AND	R3,R3,#0	; R3 = 0
	ADD	R1,R3,#4	; R1 = 4
	LEA	R0,MSG2
	PUTS
LP1	GETC
	OUT
	ADD	R0,R0,R5	; R0 = R0 - '0'
	BRn	TRYAGN
	ADD	R6,R0,#-10
	BRn	OKAT1
	ADD	R0,R0,#-7	; R0 = R0 - 7
	BRn	TRYAGN
	ADD	R6,R0,#-10
	BRn	TRYAGN
	ADD	R6,R0,#-16
	BRn	OKAT1	
	ADD	R0,R0,#-16
	ADD	R0,R0,#-16
	ADD	R6,R0,#-10
	BRn	TRYAGN
	ADD	R6,R0,#-16
	BRzp	TRYAGN
OKAT1	ADD	R3,R3,R3
	ADD	R3,R3,R3
	ADD	R3,R3,R3
	ADD	R3,R3,R3
	ADD	R3,R3,R0
	ADD	R1,R1,#-1
	BRp	LP1

	AND	R4,R4,#0	; R3 = 0
	ADD	R1,R4,#4	; R1 = 4
	LEA	R0,MSG3
	PUTS
LP2	GETC
	OUT
	ADD	R0,R0,R5	; R0 = R0 - '0'
	BRn	TRYAGN
	ADD	R6,R0,#-10
	BRn	OKAT2
	ADD	R0,R0,#-7	; R0 = R0 - 7
	BRn	TRYAGN
	ADD	R6,R0,#-10
	BRn	TRYAGN
	ADD	R6,R0,#-16
	BRn	OKAT2	
	ADD	R0,R0,#-16
	ADD	R0,R0,#-16
	ADD	R6,R0,#-10
	BRn	TRYAGN
	ADD	R6,R0,#-16
	BRzp	TRYAGN
OKAT2	ADD	R4,R4,R4
	ADD	R4,R4,R4
	ADD	R4,R4,R4
	ADD	R4,R4,R4
	ADD	R4,R4,R0
	ADD	R1,R1,#-1
	BRp	LP2

;; If you get to this point, you have the two numbers loaded in R3 and R4
	LEA	R6,STACK
	STR	R6,R6,#2	; Set dynamic link
	STR	R3,R6,#3	; Store argument one
	STR	R4,R6,#4	; Store argument two
	LD	R0,SUBR
	JSRR	R0,#0

	LEA	R0,MSG4
	PUTS
	LDR	R3,R6,#0

	AND	R5,R5,#0
	ADD	R4,R5,#4
PLOOP1	AND	R0,R0,#0
	ADD	R7,R5,#4
PLOOP2	ADD	R0,R0,R0
	ADD	R3,R3,#0
	BRzp	NTNEG
	ADD	R0,R0,#1
NTNEG	ADD	R3,R3,R3
	ADD	R7,R7,#-1
	BRp	PLOOP2
	ADD	R7,R0,#-10
	BRzp	PRHEX
	LD	R7,ASC0
	BRnzp	PRALL
PRHEX	LD	R7,ASCAM10
PRALL	ADD	R0,R0,R7
	OUT
	ADD	R4,R4,#-1
	BRp	PLOOP1

	HALT

TRYAGN
	LEA	R0,MSGERR
	PUTS
	BRnzp	L8MAIN
MASC0	.FILL	#-48
ASC0	.FILL	#48
ASCAM10	.FILL	#55
SUBR	.FILL	x3000
MSG1	.STRINGZ	"\nEnter ALL requested values as 4 digit hexadecimal numbers\n"
MSG2	.STRINGZ	"\nEnter First Number   "
MSG3	.STRINGZ	"\nEnter Second Number  "
MSG4	.STRINGZ	"\nResult (in hex) is   "
MSGERR	.STRINGZ	"\nBad number -- try again\n\n"
STACK	.BLKW	100
	.END