sub comp {
   my ($qfn1, $qfn2) = @_;

   open(my $fh1, '<:raw:stdio', $qfn1)
      or die("Unable to open file \"$qfn1\": $!\n");
   open(my $fh2, '<:raw:stdio', $qfn2)
      or die("Unable to open file \"$qfn2\": $!\n");

   my $size1 = -f $fh1 && -s _;
   my $size2 = -f $fh2 && -s _;
   return 0 if $size1 && $size2 && $size1 != $size2;

   local $/ = \(16*1024);
   for (;;) {
      my $blk1 = <$fh1>;
      my $blk2 = <$fh2>;
      return 0 if defined($blk1) xor defined($blk2);
      return 1 if !defined($blk1);
      return 0 if if $blk1 ne $blk2;
   }
}