#!/usr/bin/perl

# Latest perl version with the newest features and bugfixes
use v5.40;

# Do all kinds of automatic checking of the program code
use strict;
use warnings;

# Great debugging tool to quickly print a complex structure (array, hash, scalar, whatever) to the console
use Data::Dumper;

# Call the calculation main routine
my $max = 100; # 4_000_000;
my @baseframe = (1, 2, 3);
my $result = fib($max, \@baseframe); # Call with a REFERENCE to @baseframe, so subs can modify it

# Print the final result
print 'Final: ', $result, "\n";

# For debugging, print the final state of @baseframe
print 'Final @baseframe: ', Dumper(\@baseframe), "\n";

# And end scene...
exit(0);


# This does ONE round of the calculation, no deep recursion
sub fib_one_round($frame) {
    $frame->[0] = $frame->[0] + $frame->[1];
    $frame->[1] = $frame->[2];
    $frame->[3] = $frame->[2];

    if(($frame->[0] %2) != 0) {
        return $frame->[0];
    }

    return 0;
}

# This does the main loop. We are working on an array *reference*, so fib_one_round can modify the array
sub fib($max, $frame = [1, 2, 3]) {
    my $result = 0;

    # Loop until the max value has been reached
    while($result < $max) {
        $result += fib_one_round($frame);

        # Print the intermediate results for debugging
        print $result, "\n";
    }

    return $result;
}