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dpavlin |
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#!/usr/bin/perl -w |
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# calc.pl |
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# |
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# 04/22/07 14:29:00 CEST Dobrica Pavlinusic <dpavlin@rot13.org> |
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use strict; |
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use File::Slurp; |
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my $file = shift @ARGV || die "usage: $0 packet\n"; |
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my $p = read_file( $file ) || die "can't read $file: $!"; |
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dpavlin |
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my $orig = $1 if ( $p =~ s/(..)$//s ); |
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dpavlin |
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print "ORIGINAL checksum: $orig\n"; |
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my $sum = 0; |
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for my $i ( 0 .. length($p) ) { |
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my $c = substr($p,$i,1); |
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my $o = ord($c); |
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dpavlin |
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my $h = sprintf('%02x',$o); |
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dpavlin |
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# $sum += $o; |
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$sum ^= $o; |
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dpavlin |
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printf("# %-2d '%s' %2d %02x -- %2d %02d\n", $i,$c,$o,$o,$sum,$sum); |
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dpavlin |
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} |
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dpavlin |
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printf("checksum: %s == %02x\n", $orig, $sum); |