use DB_File;
my $hash;
tie %hash, DB_File, "first_file.hash";
while (<FIRST_FILE>)
{
  $hash{$_} = undef;
}

while (<SECOND_FILE>)
{
  print $_ if exists $hash{$_};
}

##</code><code>##

my $h = 0;
foreach (split("", $line)) {
  $h+=ord($_)
}
$h = $h % 256;

##</code><code>##

file1/0
file1/1
...
file1/255
file2/0
file2/1
...
file2/255