ernie.WPI.EDU> cat class17c.C

// file class17b.C, cs2223, D97/98 //
// Fibonacci sequence using lookup table

// 09Apr08 NW, First version

// includes
#include "n_int.h" // Class 2, Problem 1, and Problem 2
#include "Timer.h" // see Class 2

// definitions
#define FIB_MAX 1000

// prototype
n_int fib(int); // Fibonacci sequence

// main
int main ()
	{
	Timer *timer;
	timer = new Timer(1);
	cout << "fib(" << FIB_MAX  <<") =" << endl;
	(fib(FIB_MAX).print(75)); // calculate and print a big fibonacci number
	delete timer; // print out the time
	cout << endl;
	
	timer = new Timer(2);
	for (int n = 0; n <= 1000; n++) fib(FIB_MAX); // call the function 1000 times
	delete timer; // print out the time
	return 0;
	} // end main()

n_int fib(int n) // Fibonacci sequence
	{
	static n_int fib[FIB_MAX + 1]; // be careful, this can become BIG
	static int first_time = 1;
	static int size = -1; // the last value calculated
	static n_int error;
	if (first_time) // initialize the array
		{
		(fib[0]).make(0);
		(fib[1]).make(1);
		size = 1;
		error.make(0);
		first_time = 0;
		}
	if (n > FIB_MAX) return error; // too big
	if (n < 0) return error; // too small
	if (n > size) // calculate only what is needed, but remember it
		{
		for (int m = size+1; m <= n; m++) fib[m] = fib[m-1] + fib[m-2];
		size = n;
		}
	return fib[n];
	} // end fib()

// Copyright 1998 Norman Wittels

ernie.WPI.EDU> g++ class17c.C Timer.C n_int.C

ernie.WPI.EDU> a.out

fib(1000) =
434665576869374564356885276750406258025646605173717804024817290895365554179
490518904038798400792551692959225930803226347752096896232398733224711616429
96440906533187938298969649928516003704476137795166849228875
Process 1 took 1.09996 seconds

Process 2 took 0.099996 seconds

ernie.WPI.EDU>