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net:   0 0 0 0 1 0 1 0 1 1 0 1 1 1 1 1 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0
mask: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 0 0 0 0 0
key:  1010101011101110111110111111111110101010101011000000000000000000

#!/usr/bin/perl
use DB_File;
...
    my ($n,$m,$b)     = map { unpack"N",$_} $addr,$mask,$addr|~$mask;
    $ip >= $n && $ip <= $b;
}