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I was recently enjoying(sic) seeing 'script kiddies' trying
to scan the ports on my home box. I wrote a script to
parse out the packet DENY entries from my messages
log file and realized that I should sort the list of
IP's to make them easier to read.
Thoughts of complex sorting started to form in my head: split up the quad's and start comparing. I started to look for some elegant ways of doing this, when I realized how much more simple (and potentially more efficient) it would be to pack each IP into it's hex form. "This has to be a much, much faster way", I thought to myself. So I did a search at Google and found this page written by Uri Guttman and Larry Rosler. They discuss this very thing - giving one example that sorts by breaking up the IP bytes and comparing them, and another example that packs the IP's into hex. Here are their two examples, slightly paraphrased: What gets me is the fact that they have the same Big(O), but when benchmarked: there is an obvious difference. To be honest, I really hated Big(O)analysis in college, and I think this is the very reason why. There is an obvious amount of better efficiency in the packed version, but in a constant way - this of course is eliminated when doing Big(O), making both algorithms 'equal'. I am posting this mainly because I couldn't find any good IP sorting algorithms on PM, but I was also wondering how other Monks out there feel about the Big(O).
Jeff Anderson
UPDATE: Fri Aug 4 09:31:30 CDT 2000 In reply to Sorting a list of IP addresses (aka Why I hate Big O) by jeffa
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