#!/usr/bin/env perl
use utf8;
###############################################################################
# Program computes a simple checksum of STDIN
# 
# Copyright © 2017 Richard Lesh.  All rights reserved.
###############################################################################

use Utils;
use strict;
use warnings;

MAIN:
{
    binmode(STDIN);
    my $c;
    my $temp = 0;
    my $count = 0;
    my $checksum = 0;
    while (defined($c = Utils::getbyte(*STDIN))) {
        $temp = $c;
        $temp = Utils::lshift32($temp, (3 - ($count % 4)) * 8);
        $checksum = Utils::bitwiseXOr32($checksum, $temp);
        ++$count;
    }
    my $result = Utils::toHex($checksum);
    print substr($result, -8), "\n";
}