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#!/usr/bin/perl
#
# Construct a checksum for isolinux*.bin, compatible
# with an mkisofs boot-info-table
#
use bytes;
use integer;
($file) = @ARGV;
open(FILE, '+<', $file) or die "$0: cannot open $file: $!\n";
binmode FILE;
@fstat = stat(FILE) or die "$0: stat $file: $!\n";
if (!$fstat[7]) {
die "$0: $file: cannot query length\n";
}
# Pad file to a multiple of 2048 bytes
$frac = $fstat[7] % 2048;
if ($frac) {
seek(FILE,$fstat[7],0)
or die "$0: $file: cannot seek to end\n";
print FILE "\0" x (2048-$frac);
}
# Checksum the file post header
if ( !seek(FILE,64,0) ) {
die "$0: $file: cannot seek past header\n";
}
$csum = 0;
$bytes = 64;
while ( ($n = read(FILE, $dw, 4)) > 0 ) {
$dw .= "\0\0\0\0"; # Pad to at least 32 bits
($v) = unpack("V", $dw);
$csum = ($csum + $v) & 0xffffffff;
$bytes += $n;
}
# Update header
if ( !seek(FILE,16,0) ) {
die "$0: $file: cannot seek to header\n";
}
print FILE pack("VV", $bytes, $csum);
close(FILE);
exit 0;
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