COMP1721 - Higher Computing 1B

1. 
   main:
       LDI    r24, 10 
       LDI    r31, hi8(pm(fib))  
       LDI    r30, lo8(pm(fib)) 
       ICALL
       MOV    r26, r24
       LDI    r24, 1     ; print "%d\n"
       LDI    r31, 0x70  
       LDI    r30, 0x00  
       ICALL
       LDI    r24, 0     ; exit
       LDI    r31, 0x70  
       LDI    r30, 0x00  
       ICALL
   fib:
   ; if (n < 2) return 1;
   	LDI    r16, 1   
   	SUB    r16, r24
       BRBS   2, L1
   	LDI    r24, 1
   	RET
   L1:
   ; save n on stack
   	PUSH   r24
   ; calculate fib(n-1)
   	LDI    r16, 1
   	SUB    r24, r16
       LDI    r31, hi8(pm(fib))  
       LDI    r30, lo8(pm(fib))
       ICALL
   ; recover n and save fib(n-1) to stack
   	POP    r16
       PUSH   r24
       MOV    r24, r16
   ; calculate fib(n-2)
   	LDI    r16, 2
   	SUB    r24, r16
       LDI    r31, hi8(pm(fib))  
       LDI    r30, lo8(pm(fib))
       ICALL
   ; recover fib(n-1)
   	POP    r16
   	ADD    r24, r16
   ; return fib(n-1)+fib(n-2)
   	RET