; Gatlin Johnson
; HW #8
; 17 April 2009
; 
; fib-8.asm

.ORIG x3000

MAIN
	LD  R6, STACKSTART			;  load start of stack

; Put initial call to fibonacci here

	ADD R5, R6, -1
	ADD R6, R6, -1

	AND R1, R1, 0
	;ADD R1, R1, 5
	LD R1, INPUT
	
	ADD R6, R6, -1
	STR R1, R6, 0

	JSR FIB

	LDR R1, R6, 0
	
	ST R1, OUTPUT
	
	ADD R6, R6, 1

	ADD R6, R6, 1
FUN_END
HALT

;;; FIB function definition
FIB
	ADD R6, R6, -1
	ADD R6, R6, -1
	STR R7, R6, 0
	ADD R6, R6, -1
	STR R5, R6, 0

	ADD R6, R6, -1
	ADD R5, R6, 0
	
	STR R1, R6, -1
	STR R2, R6, -2
	STR R3, R6, -3
	ADD R6, R6, -3
	
	; actual function starts here
	LDR R1, R5, 4

	; strategy: if it's greater than 0 or 1, RECURSE
	; otherwise, just store 1 in R2
	
	AND R3, R3, 0
	ADD R3, R1, -2
	BRp RECURSE
	
	; we got here, so just stick a 1 in
	AND R2, R2, 0

	ADD R2, R2, 1

FINISH_FIB
	STR R2, R5, 3
	ADD R6, R6, 3
	LDR R3, R6, -3
	LDR R2, R6, -2
	LDR R1, R6, -1

	ADD R6, R6, 1
	LDR R5, R6, 0
	ADD R6, R6, 1

	LDR R7, R6, 0
	ADD R6, R6, 1

	RET

RECURSE
	AND R3, R3, 0
	AND R2, R2, 0

	ADD R6, R6, -1
	ADD R2, R1, -1

	STR R2, R6, 0
	JSR FIB
	LDR R3, R6, 0
	ADD R6, R6, 1
	ADD R6, R6, 1

	AND R2, R2, 0

	ADD R6, R6, -1
	ADD R2, R1, -2
	STR R2, R6, 0
	JSR FIB
	LDR R2, R6, 0
	ADD R6, R6, 1
	ADD R6, R6, 1

	ADD R2, R3, R2

	BR FINISH_FIB

STACKSTART .FILL xd000
INPUT      .FILL x16DA
OUTPUT     .FILL x0000
.END