/*************************************************************************
Fibonacci
In a Fibonacci series each number is the sum of the two previous numbers. 
This program calculates Fibonacci numbers within an 8-bit range,
Files c018i.o and p18f2420.lib are included by the Linker Script. 
Program intended for simulation only, hence no input/output.
TJW 21.10.05						retested 23.5.09
;************************************************************************/

#include <p18f2420.h>

//these memory locations hold the Fibonacci series
unsigned char fib0;	//lowest number 
			//(oldest when going up, newest when reversing down)
unsigned char fib1; 	//middle number
unsigned char fib2; 	//highest number
unsigned char fibtemp;  //temporary location for newest number
unsigned char counter;  //indicates which value series has reached

void main (void) 
{	
 fib0 = 0;
 fib1 = 1;
 fib2 = 1;
 counter = 3; //have preloaded the first three numbers, so start at 3
loop:
do 
	{
fibtemp = fib1 + fib2;
	counter = counter + 1;
//now shuffle numbers held, discarding the oldest
	fib0 = fib1; 	//first move middle number, to overwrite oldest
	fib1 = fib2;
	fib2 = fibtemp;
	}
	while (counter<12);
//when reversing down, we will subtract fib0 from fib1 to form new fib0
	do 
	{
fibtemp = fib1 - fib0;  //latest number now placed in fibtemp
	counter = counter - 1; 
//now shuffle numbers held, discarding the oldest
	fib2 = fib1; 	//first move middle number, to overwrite oldest
	fib1 = fib0;
	fib0 = fibtemp;
	}
	while (fib0>0); 
	goto loop;
}