.ORIG x3000

	JUMP MAIN

; ------------------------------------------------------

; Main Function

; Register Assignments:
;	R5 - Return Value
;	R6 - Stack Pointer
;	R7 - Return Address

ASCII_172	.STRINGZ "172"
ASCII_9		.STRINGZ "9"
ASCII_M43	.STRINGZ "-43"		
ASCII_M17	.STRINGZ "-17"			
		
MAIN
	;; + 172
	LD R0, TOTAL
	LEA R1, BUF
	LD R2, BUFSIZE
	JSR ITOA
	LEA R0, BUF
	TRAP x22		; PUTS

	LEA R1, ASCII_172
	LEA R0, BUF
	JSR STRCPY
	JSR ATOI

	LD R0, TOTAL
	ADD R0, R0, R1
	ST R0, TOTAL
	
	LD R0, ASCII_PLUS
	TRAP x21		; PUTC
	LEA R0, BUF
	TRAP x22		; PUTS
	LD R0, ASCII_NL
	TRAP x21		; PUTC

	;; * 9
	LD R0, TOTAL
	LEA R1, BUF
	LD R2, BUFSIZE
	JSR ITOA
	LEA R0, BUF
	TRAP x22		; PUTS

	LEA R1, ASCII_9
	LEA R0, BUF
	JSR STRCPY
	JSR ATOI

	LD R0, TOTAL
	MUL R0, R0, R1
	ST R0, TOTAL

	LD R0, ASCII_STAR
	TRAP x21		; PUTC
	LEA R0, BUF
	TRAP x22		; PUTS
	LD R0, ASCII_NL
	TRAP x21		; PUTC

	;; - -43
	LD R0, TOTAL
	LEA R1, BUF
	LD R2, BUFSIZE
	JSR ITOA
	LEA R0, BUF
	TRAP x22		; PUTS

	LEA R1, ASCII_M43
	LEA R0, BUF
	JSR STRCPY
	JSR ATOI

	LD R0, TOTAL
	SUB R0, R0, R1
	ST R0, TOTAL

	LD R0, ASCII_MINUS
	TRAP x21		; PUTC
	LEA R0, BUF
	TRAP x22		; PUTS
	LD R0, ASCII_NL
	TRAP x21		; PUTC

	;; / -17
	LD R0, TOTAL
	LEA R1, BUF
	LD R2, BUFSIZE
	JSR ITOA
	LEA R0, BUF
	TRAP x22		; PUTS

	LEA R1, ASCII_M17
	LEA R0, BUF
	JSR STRCPY
	JSR ATOI

	LD R0, TOTAL
	JSR DIV
	ST R2, TOTAL

	LD R0, ASCII_SLASH
	TRAP x21		; PUTC
	LEA R0, BUF
	TRAP x22		; PUTS
	LD R0, ASCII_NL
	TRAP x21		; PUTC

	;; Final answer 
	LD R0, TOTAL
	LEA R1, BUF
	LD R2, BUFSIZE
	JSR ITOA
	LEA R0, BUF
	TRAP x22		; PUTS
	HALT
	
PROMPT	.STRINGZ "calc:"
BYE	.STRINGZ "bye!"
ERROR	.STRINGZ "error!"	
BUF	.BLKW #16
BUFSIZE	.FILL #16
TOTAL	.FILL x0000	
	
ASCII_SPACE	.FILL x0020

ASCII_STAR	.FILL x002A
ASCII_PLUS	.FILL x002B
ASCII_MINUS	.FILL x002D
ASCII_SLASH     .FILL x002F

ASCII_0		.FILL x0030

ASCII_NL	.FILL x000A	
	
;;; DIV (divide) - divide one integer by another
;;; Inputs:	R0 - dividend
;;;		R1 - divisor
;;; Outputs:	R2 - quotient
;;;		R3 - remainder
DIV
	INC R6, #-1
	STR R4, R6, #0

	BRnp R1, DIV_NOTBYZERO
	AND R1, R0, R0
	LEA R0, ERROR
	TRAP x22		; PUTS
	AND R0, R1, R1
	CONST R1, #0
	JUMP DIV_DONE
DIV_NOTBYZERO
		
	CONST R2, #0
	AND R3, R0, R0
	BRn R0, DIV_N		
DIV_P
	BRn R1, DIV_PN		; Positive dividend
DIV_PP				; Divide positive by positive
	SUB R4, R3, R1
	BRn R4, DIV_DONE
	INC R2, #1
	SUB R3, R3, R1
	JUMP DIV_PP
DIV_PN				; Divide positive by negative 
	ADD R4, R3, R1
	BRn R4, DIV_DONE
	INC R2, #-1
	ADD R3, R3, R1
	JUMP DIV_PN
DIV_N				; Negative dividend
	BRn R1, DIV_NN
DIV_NP				; Divide negative by positive
	ADD R4, R3, R1
	BRp R4, DIV_DONE
	INC R2, #-1
	ADD R3, R3, R1
	JUMP DIV_NP
DIV_NN				; Divide negative by negative
	SUB R4, R3, R1
	BRp R4, DIV_DONE
	INC R2, #1
	SUB R3, R3, R1
	JUMP DIV_NN

DIV_DONE
	LDR R4, R6, #0
	INC R6, #1
	JUMPR R7
;;; ATOI (ascii to integer) - converts well-formed integer string to integer
;;; Inputs:	R0 - pointer to null terminated string
;;; Outputs:	R1 - integer
ATOI
	INC R6, #-5
	STR R0, R6, #0
	STR R2, R6, #1
	STR R3, R6, #2
	STR R4, R6, #3
	STR R7, R6, #4

	CONST R1, #0		; Initialize return value to 0
	
	LDR R4, R0, #0
	LD R3, ASCII_MINUS
	SUB R4, R4, R3		; R4 will be zero if number is negative
	BRnp R4, ATOI_LOOP
	INC R0, #1

ATOI_LOOP
	LDR R2, R0, #0
	BRz R2, ATOI_LOOP_DONE
	CONST R3, #10
	MUL R1, R1, R3		; Found another digit, multiply return value by 10
	LD R3, ASCII_0
	SUB R3, R2, R3
	ADD R1, R1, R3		; Add new digit
	INC R0, #1
	JUMP ATOI_LOOP
ATOI_LOOP_DONE

	BRnp R4, ATOI_DONE	; If there was a minus sign, negate the number
	NOT R1, R1
	INC R1, #1

ATOI_DONE
	LDR R7, R6, #4
	LDR R4, R6, #3
	LDR R3, R6, #2
	LDR R2, R6, #1
	LDR R0, R6, #0
	INC R6, #5
	JUMPR R7
	
;;; ITOA (integer to ascii) - converts well-formed integer string to integer
;;; Inputs:	R0 - integer
;;;		R1 - pointer to null terminated string
;;;		R2 - length of string
ITOA

	INC R6, #-7
	STR R0, R6, #0
	STR R1, R6, #1
	STR R2, R6, #2
	STR R3, R6, #3
	STR R4, R6, #4
	STR R5, R6, #5
	STR R7, R6, #6

	CONST R5, #0		; First, calculate output string length

	CONST R1, #10
	
	BRzp R0, ITOA_LENGTH_LOOP
	INC R5, #1		; length++ for the minus sign

ITOA_LENGTH_LOOP
	INC R5, #1
	JSR DIV
	AND R0, R2, R2
	BRnp R2, ITOA_LENGTH_LOOP

	LDR R2, R6, #2		; Check for buffer overflow
	SUB R7, R2, R5
	INC R7, #-1
	BRn R7, ITOA_DONE
	
	LDR R0, R6, #0
	LDR R4, R6, #1

	BRzp R0, ITOA_LOOP_HEADER
	LD R7, ASCII_MINUS	; Write the minus sign
	STR R7, R4, #0
	NOT R0, R0		; Negate the number
	INC R0, #1
	
ITOA_LOOP_HEADER
	CONST R1, #10
	ADD R4, R4, R5		; Write the number right-to-left (it's easier)
	CONST R7, #0
	STR R7, R4, #0		; Write the null terminator

ITOA_LOOP
	JSR DIV
	LD R7, ASCII_0
	ADD R7, R3, R7		; Write remainder
	INC R4, #-1
	STR R7, R4, #0
	AND R0, R2, R2		; Copy quotient to dividend
	BRp R0, ITOA_LOOP

ITOA_DONE
	LDR R7, R6, #6
	LDR R5, R6, #5
	LDR R4, R6, #4
	LDR R3, R6, #3
	LDR R2, R6, #2
	LDR R1, R6, #1
	LDR R1, R6, #0
	INC R6, #7
	JUMPR R7	

;;; STRCPY (string copy) - length-unchecked copy of null terminated string to buffer
;;; Inputs:	R0 - pointer to buffer
;;;		R1 - pointer to null terminated string
;;; Outputs:	none		
STRCPY	
	INC R6, #-3
	STR R0, R6, 0
	STR R1, R6, 1
	STR R2, R6, 2

STRCPY_LOOP
	LDR R2, R1, 0
	STR R2, R0, 0
	BRz R2, STRCPY_DONE
	INC R1, #1
	INC R0, #1
	JUMP STRCPY_LOOP
STRCPY_DONE		
			
	LDR R2, R6, 2
	LDR R1, R6, 1
	LDR R0, R6, 0
	JUMPR R7