1 package C4::SIP::Sip::Checksum;
7 our @ISA = qw(Exporter);
8 our @EXPORT_OK = qw(checksum verify_cksum);
13 return (-unpack('%16C*', $pkt) & 0xFFFF);
21 if ($pkt =~ /AZ(....)$/) {
22 $debug and warn "verify_cksum: sum ($1) detected";
24 warn "verify_cksum: no sum detected";
25 return 0; # No checksum at end
27 # return 0 if (substr($pkt, -6, 2) ne "AZ");
29 # Convert the checksum back to hex and calculate the sum of the
30 # pack without the checksum.
32 $shortsum = unpack("%16C*", substr($pkt, 0, -4));
34 # The checksum is valid if the hex sum, plus the checksum of the
35 # base packet short when truncated to 16 bits.
36 return (($cksum + $shortsum) & 0xFFFF) == 0;
43 # Some simple test data
47 my $cksum = checksum($testpkt);
48 my $fullpkt = sprintf("%s%4X", $testpkt, $cksum);