hey,
I'm trying to write a traffic checker of a Switch port via SNMP.

I wrote it using AnyEvent::SNMP timer, and OID that gives the bytes out of the required port.
My problem is when the previous result is bigger than the current result.
As I understood, I need to add 0xffffffff to the negative result,
but I get a wrong result, something that is definitely not the result I calculated... What am I doing wrong?

That's my code:

use AnyEvent;
use AnyEvent::SNMP;
use Net::SNMP;
use Data::Dumper;

my $cv = AnyEvent->condvar;
my @watchers;
my $OID_BytesOut = '.1.3.6.1.2.1.2.2.1.16.10101';
my ($previousResult, $currentResult) = 0;
my $currentMBitsPerSecond = 0;

my ($session, $error) = Net::SNMP->session (
                    -hostname       => "127.0.0.1",
                    -community      => "yada",
                    -version        =>  2,
                    -nonblocking    =>  1,
                    );

if (!defined $session) {
        print "ERROR creating session: $error.\n";
        exit 1;
}

push @watchers, AnyEvent->timer(
    after       => 0,
    interval    => 1.0,
    cb          => sub {
        $session->get_request(
            -varbindlist    =>  [ $OID_BytesOut ],
            -callback       =>  [ \&SNMP_get_handler ] );

        if (defined $previousResult && defined $currentResult) {
            if ( $previousResult < $currentResult) {
                $currentMBitsPerSecond = 
                    ((($currentResult - $previousResult) /1024) / 1024
+) * 8;
            }
            else {
                my $tempCalculation = 
                    ($currentResult - $previousResult) + 0xffffffff;
                $currentMBitsPerSecond = 
                    ((($tempCalculation) / 1024) / 1024) * 8;
            }
        }

        $currentMBitsPerSecond = int($currentMBitsPerSecond);
        if ( $currentMBitsPerSecond > 0) {
            print "$currentMBitsPerSecond Mbit/s\n";
        }
    }
);

sub SNMP_get_handler {
    my $session = shift;

    my $host = $session->hostname;
    my $results = $session->var_bind_list;

    if(!defined $results) {
        printf("ERROR getting result: %s.\n", $session->error());
    }

    if (defined $currentResult) {
        $previousResult = $currentResult;
    }

    $currentResult = $results->{$OID_BytesOut};
}

$cv->wait;
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