This post is prompted by another XKCD Comic sent by my son.
If you pride yourself on being a bit nerdy and still don't get this cartoon don't despair, because this is pretty esoterically nerdy. It also relates to why my high score in Tetris is -21,504 (yes, that's a negative sign). Even though jokes that have to be explained generally aren't that funny, if you don't get this and want to learn more (and learn more about my Tetris habit) read on.
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When computers represent integers they can do so with single-precision (16 bit, or short integer) or double-precision (32 bit, or long integer) numbers. In the olden days when memory was expensive and computer programmers actually had to pay attention to writing more compact code, this distinction mattered more (as in saving memory usage by using single-precision numbers). The largest single-precision integer that a computer can represent is 2 to the 15th power minus 1 (counting starts from 0, not 1), or 32,767 (see cartoon). If a computation results in a number bigger than that, rather than generate an error, the number "wraps" and starts counting back toward 0, but now with a negative sign (again, see comic). That comic is pretty funny, now, right...? (Even more funny, if you go to the cartoon at the XKCD website and hover the mouse cursor over the comic, you'll bring up a caption with a computer programming reference to the Philip K. Dick short story "Do Androids Dream of Electric Sheep?", which is the basis for the movie Bladerunner.)
Now how does this relate to Tetris? I am a fan of simple-minded games like Minesweeper and Tetris (my day job provides enough complicated action that complicated games are just not that appealing). As I began to get higher scores when I first started playing Tetris, one day I couldn't suppress the nerdy side of my brain and I began to wonder whether the person who coded Tetris thought to use a double-precision integer (which can go up to 2,147,483,657) to keep track of the score, or whether they used single precision. So, I pressed on trying to get a score high enough to answer this question and, finally, I got a score that hit 32,767 and wrapped -- voilà, it was coded using single-precision integer arithmetic! For some reason it was incredibly satisfying to me to have answered this question. As I continue to play Tetris I keep pushing my score, but I've only managed to get to -21,504. Simple pleasures...what can I say?
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