#!/usr/bin/env perl
use strict;
use warnings;
use Time::HiRes qw( gettimeofday tv_interval );

for my $i (1 .. 100) {
    my $start = [gettimeofday];
    my $fibonacci_number = fibo($i);
    my $interval = tv_interval( $start, [gettimeofday]);
    print "fib($i)=$fibonacci_number  ($interval sec)\n";
}

sub fibo {
    my $num = shift;
    return 1 if $num<3;
    return fibo($num-1) + fibo($num-2);
}

##</code><code>##

$ perl fibo.pl
fib(1)=1  (6e-06 sec)
fib(2)=1  (4e-06 sec)
fib(3)=2  (7e-06 sec)
fib(4)=3  (6e-06 sec)
fib(5)=5  (6e-06 sec)
fib(6)=8  (1e-05 sec)
fib(7)=13  (1.6e-05 sec)
fib(8)=21  (2.4e-05 sec)
fib(9)=34  (3.5e-05 sec)
fib(10)=55  (5.6e-05 sec)
fib(11)=89  (8.9e-05 sec)
fib(12)=144  (0.000145 sec)
fib(13)=233  (0.000291 sec)
fib(14)=377  (0.000379 sec)
fib(15)=610  (0.000609 sec)
fib(16)=987  (0.000981 sec)
fib(17)=1597  (0.001583 sec)
fib(18)=2584  (0.002644 sec)
fib(19)=4181  (0.00414 sec)
fib(20)=6765  (0.005748 sec)
fib(21)=10946  (0.004466 sec)
fib(22)=17711  (0.007214 sec)
fib(23)=28657  (0.011702 sec)
fib(24)=46368  (0.018114 sec)
fib(25)=75025  (0.027751 sec)
fib(26)=121393  (0.045355 sec)
fib(27)=196418  (0.072849 sec)
fib(28)=317811  (0.117512 sec)
fib(29)=514229  (0.193195 sec)
fib(30)=832040  (0.307089 sec)
fib(31)=1346269  (0.505429 sec)
fib(32)=2178309  (0.796903 sec)
fib(33)=3524578  (1.312573 sec)
fib(34)=5702887  (2.093858 sec)
fib(35)=9227465  (3.422112 sec)
fib(36)=14930352  (5.594139 sec)
fib(37)=24157817  (8.969398 sec)
fib(38)=39088169  (14.46981 sec)
fib(39)=63245986  (23.423682 sec)
fib(40)=102334155  (38.201329 sec)
fib(41)=165580141  (62.30559 sec)
^C

##</code><code>##

use Memoize;
memoize('fibo');

##</code><code>##

$ perl fibo.pl
fib(1)=1  (8e-06 sec)
fib(2)=1  (5e-06 sec)
fib(3)=2  (1.2e-05 sec)
fib(4)=3  (7e-06 sec)
fib(5)=5  (6e-06 sec)
fib(6)=8  (6e-06 sec)
fib(7)=13  (6e-06 sec)
fib(8)=21  (6e-06 sec)
fib(9)=34  (5e-06 sec)
fib(10)=55  (6e-06 sec)

 . . . <snip> . . .

fib(98)=1.35301852344707e+20  (6e-06 sec)
fib(99)=2.18922995834555e+20  (6e-06 sec)
fib(100)=3.54224848179262e+20  (6e-06 sec)