|No such thing as a small change|
Sorting a list of IP addresses (aka Why I hate Big O)by jeffa (Bishop)
|on Aug 03, 2000 at 00:15 UTC||Need Help??|
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).
UPDATE: Fri Aug 4 09:31:30 CDT 2000