#!/usr/bin/perl

use warnings;
use strict;

sub makeBitstream {
    my $lenarr = $#_ + 1;
    if ($lenarr % 2) {
        die "Uneven number of elements in array.";
    }
    my @l = ();
    my $i;
    my $x = 0;
    while ($x < $lenarr / 2) {
        push(@l, shift(@_));
        $x++;
    }
    my @v = @_;
    my $bitstream = "";
    for ($i=0; $i<=$#v; $i++) {
        my $s = "%0" . $l[$i] ."b";
        $bitstream .= sprintf("$s", $v[$i]);
    }
    return $bitstream;
}

sub makeThreeBytes {
    my $bitstream = shift;
    my $i;
    my @listOfBytes = (substr($bitstream, 0, 8),
                       substr($bitstream, 8, 8),
                       substr($bitstream, 16, 8));
    for ($i=0; $i<=$#listOfBytes;$i++) {
        $listOfBytes[$i] = oct("0b". $listOfBytes[$i]);
    }
    return @listOfBytes;
}

my $bitstream = makeBitstream(5, 1, 10, 8, 2, 0, 64, 2);
my @listOfBytes = makeThreeBytes($bitstream);

my $i;
my $checksum = 0;
foreach $i (@listOfBytes) {
    $checksum += $i;
}
print "$checksum\n";

if ($checksum > 511) {
    $checksum -= 512;
}
if ($checksum > 255) {
    $checksum -= 256;
}
if ($checksum > 127) {
    $checksum -= 128;
}

print "$checksum\n";

my $bits = makeBitstream(5, 1, 10, 8, 8, 2, 0, 64, 2, $checksum);
print "$bits\n";