mdap/protocol/calc.pl

#!/usr/bin/perl -w

# calc.pl
#
# 04/22/07 14:29:00 CEST Dobrica Pavlinusic <dpavlin@rot13.org>

use strict;
use File::Slurp;

my $file = shift @ARGV || die "usage: $0 packet\n";

my $p = read_file( $file ) || die "can't read $file: $!";

my $orig = $1 if ( $p =~ s/(..)$//s );

print "ORIGINAL checksum: $orig\n";

my $sum = 0;
for my $i ( 0 .. length($p) ) {
        my $c = substr($p,$i,1);
        my $o = ord($c);
        my $h = sprintf('%02x',$o);
#       $sum += $o;
        $sum ^= $o;
        printf("# %-2d '%s' %2d %02x -- %2d %02d\n", $i,$c,$o,$o,$sum,$sum);
}

my $xor = 0;
map { $xor ^= ord($_) } split(//,$p);

printf("checksum: %s == %02x [xor=%02x]\n", $orig, $sum, $xor);
1	dpavlin	11	#!/usr/bin/perl -w
2
3			# calc.pl
4			#
5			# 04/22/07 14:29:00 CEST Dobrica Pavlinusic <dpavlin@rot13.org>
6
7			use strict;
8			use File::Slurp;
9
10			my $file = shift @ARGV \|\| die "usage: $0 packet\n";
11
12			my $p = read_file( $file ) \|\| die "can't read $file: $!";
13
14	dpavlin	12	my $orig = $1 if ( $p =~ s/(..)$//s );
15	dpavlin	11
16			print "ORIGINAL checksum: $orig\n";
17
18			my $sum = 0;
19			for my $i ( 0 .. length($p) ) {
20			my $c = substr($p,$i,1);
21			my $o = ord($c);
22	dpavlin	12	my $h = sprintf('%02x',$o);
23	dpavlin	11	# $sum += $o;
24			$sum ^= $o;
25	dpavlin	12	printf("# %-2d '%s' %2d %02x -- %2d %02d\n", $i,$c,$o,$o,$sum,$sum);
26	dpavlin	11	}
27
28	dpavlin	13	my $xor = 0;
29			map { $xor ^= ord($_) } split(//,$p);
30
31			printf("checksum: %s == %02x [xor=%02x]\n", $orig, $sum, $xor);