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use strict;
use Socket;
...
  $chk = ($chk >> 16) + ($chk & 0xffff); # Foldhigh into low
  return(~(($chk >> 16) + $chk) & 0xffff); # Again and complement
}

  my $buff;
  defined(recv(SOCK,$buff,256,0)) or die "error: $! \n";
...
    print "not an icmp reply\n";
  }
}