I never once heard it or saw it written like that before Hacker News / proggit.
I cringed when someone on proggit recently said "Do the maths!" I don't think that's a saying anywhere.
It seems that "maths" is the semantically correct option. To take your quote, "do the math" expands to "do the mathematic" - which is surely wrong.
I don't think of code as being divisible into discrete units, it's like a fluid. Like "water", you rarely say "waters". There are "programs" and "libraries" and "frameworks" that are made up of "code" or multiple "files containing code"... but they are not "codes"!
If you want to use the word "codes", you'll need to give me an adequate definition of the word "code" as a singular noun (which I will most likely disagree with).
In my mind "code" means programming language code, and "codes" means cryptography related codes.
</rant>
http://en.wikipedia.org/wiki/Uncountable_noun
One of the funnier differences between Italian and English is that in the former, you say "hairs" - it's not uncountable, which to us sounds pretty funny, as I'm sure we do when talking about our "one hair". "My hairs are all messed up!"
I find 'plz' and 'thx' and 'tks' and '10x' and so on the most annoying though; how the fuck is it polite if you can't even be bothered to spell the complete word? If you want to show gratitude, 'thanks' or 'thank you' are much better, and english already provides 'ta' as a short form.
Sigh. People treating IRC like AOL make my sad.