#!/usr/local/bin/perl -w
# fib-memoize.pl -- Memoizing zur Beschleunigung der Fibonacci-Funktion

# Diese Version von fib() benutzt Memoizing zur Beschleunigung
{
    local %cache;
    sub fib {
    return 1 if $_[0] == 0 || $_[0] == 1;
    return $cache{$_[0]} if exists $cache{$_[0]};
    return $cache{$_[0]} = fib($_[0]-1) + fib($_[0]-2);
    }
}

# Das ist die alte, klassische rekursive fib()-Definition
sub slowfib {
    return 1 if $_[0] == 0 || $_[0] == 1;
    return slowfib($_[0] - 1) + slowfib($_[0] - 2);
}

my $big = shift;      # Argument von der Kommandozeile

use Time::HiRes qw( time );

$before = time(); $res = fib($big); $secs = time() - $before;
print "fib($big) = $res, ($secs seconds)\n";

$before = time(); $res = fib($big); $secs = time() - $before;
print "fib($big) = $res, ($secs seconds)\n";

$before = time(); $res = slowfib($big); $secs = time() - $before;
print "slowfib($big) = $res, ($secs seconds)\n";