while ( $ChecksumLoopCounter < $Size ) {
    unless ( sysread ( $FileHandle, $BufferByte, 1) == 1 ) {
        die "sysread size error" ;
    }
    my $Byte = ord($BufferByte);
    $Checksum = unpack("S" , pack("S", $Checksum + $Byte));
    $ChecksumLoopCounter++ ;
    $ChecksumByteOffset++ ;
}
close $FileHandle ;
return $Checksum;