| --- Log opened Sat Apr 20 00:00:21 2013 |
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| 02:18 | <&McMartin> | Whoa |
| 02:18 | <&McMartin> | BinHex was originally a TRS-80 technology o_O |
| 02:18 | <@celticminstrel> | :O |
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| 02:34 | <@froztbyte> | wat |
| 02:34 | <@froztbyte> | well, that kinda makes sense, actually |
| 02:34 | <@froztbyte> | "woo endianness", etc |
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| 08:39 | <&McMartin> | Hee hee |
| 08:39 | | * McMartin mounts the strangest of defenses of JavaScript |
| 08:40 | <&McMartin> | ("The problem isn't JS's implementation of closures; that, as you can see, tracks Scheme's implementation of them. The problem is that JavaScript has mutable state and uses it for loops.") |
| 08:45 | <&McMartin> | (Scheme has aliasing issues if you bind a variable in multiple closures and then set! values referenced thereby. However, named let and call-with-cthulhu-invocation do not have this problem.) |
| 08:53 | | * Alek munches some popcorn, watches on. |
| 08:55 | <&McMartin> | That's about it, really. |
| 08:55 | <&McMartin> | This is a mistake, in JS: for (i = 0; i < 10; ++i) { a[i] = function() { return i+1; }; } |
| 08:55 | <&McMartin> | Because you will find that all the functions in a return 11, because they're all referring to the same "i". |
| 08:56 | <&McMartin> | If you do the same construct in Scheme (with set! for mutation) the same thing happens, so clearly the fault is with having mutable state, not closures~ |
| 08:56 | <&McMartin> | (If you instead use tail recursion or continuation-based loops in Scheme, this does not happen because it's a new environment each time, so the problem is less likely to occur "accidentally".) |
| 09:09 | <@Azash> | McMartin: So when you create the function, it won't resolve "i+1" immediately but rather store the reference? |
| 09:16 | <&jerith> | Azash: Yes. |
| 09:16 | <&jerith> | The whole point of the closure is that the code in it only gets executed when you call it. |
| 09:17 | <&jerith> | The closure contains a reference to the external variable "i", which can be modified outside the closure. |
| 09:19 | <&jerith> | You can probably work around it by putting "local_i = i" (or whatever JS uses to create a variable in the local scope -- I don't actually know the language) and using local_i instead. |
| 09:21 | <&McMartin> | Actually you generally do it by wrapping it in another closure~ |
| 09:21 | <&McMartin> | a[i] = (function(x) { return function() { return x + 1; }; })(i); |
| 09:24 | <&jerith> | McMartin: I think that's "whatever JS uses to create a variable in the local scope".~ |
| 09:24 | <&jerith> | (Or, more accurately, it creates a local scope in which you can have a a local variable.) |
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| 14:12 | <@gnolam> | "Funny story, my first day, at my first ever games job, was at Mindscape. And I heard one of my chiptunes coming from the Production office. They'd just downloaded Moonstone (which was a Mindscape game) from a BBS..... could have been my shortest ever first job ;)" |
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| 21:13 | | * Derakon eyes Python. |
| 21:13 | <&Derakon> | I have a loop that does "for xi, yi in [(x - 1, y - 1), (x, y - 1), ...]" |
| 21:14 | <&Derakon> | I replaced it with "for dx, dy in [(-1, -1), (0, -1), ...]: xi = x + dx; yi = y + dy" and went from 2.6s to 2.45s in runtime. |
| 21:14 | <&Derakon> | WTF. |
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| 21:17 | <@froztbyte> | haha |
| 21:17 | <@froztbyte> | how many elements? |
| 21:17 | <&Derakon> | 8. |
| 21:17 | <@froztbyte> | ah, not many |
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| 21:18 | <@froztbyte> | yeah I only just did the permutation now |
| 21:18 | <&Derakon> | It's iterating over the neighboring cells to a given cell. |
| 21:18 | <@froztbyte> | weird though |
| 21:19 | <@froztbyte> | I don't know the innards well enough to tell you why :/ |
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| 21:29 | | * Derakon whips up a quick demo script. http://pastebin.com/r44rKdLx |
| 21:31 | <&Derakon> | Whoops, there's a spare 'y' in bar(); removing that makes it even faster! http://pastebin.com/n6sEEZQ6 |
| 21:45 | <&Derakon> | And fully-unrolling the loop makes it almost twice as fast: http://pastebin.com/v5g3qK5S |
| 21:46 | <@Tamber> | funroll! \o/ |
| 21:46 | <&Derakon> | Unfortunately I don't know how I'd go about applying that to the heatmap code. |
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| 22:37 | <@[R]> | http://i.imgur.com/tFdoSWq.jpg |
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| 22:54 | <@froztbyte> | .....wow |
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| 22:56 | < AnnoDomini> | What the shit. |
| 22:57 | <&McMartin> | PAIN IS YOUR FRIEND |
| 23:11 | | * RichyB giggles. |
| 23:21 | < AnnoDomini> | Indeed. There is a genetic condition that makes you unable to feel pain. Typically, these children die very early. |
| 23:22 | <&Derakon> | Oh hey, RichyB, any ideas on the optimization problem I was dealing with earlier? |
| 23:23 | <&Derakon> | Ultimately I'm trying to make this function faster: http://pastebin.com/PVYrhTxm |
| 23:32 | <@EvilDarkLord> | Derakon: If you want to optimize on that level, then some comparisons on 50-51 are unnecessary depending on dx and dy. For example, coordinates resulting from positive dx/dy never have to be checked for being at least 0. |
| 23:32 | <&Derakon> | Isn't checking if dx >= 0 equivalent in cost to checking if neighbor[0] >= 0? |
| 23:33 | <&Derakon> | I mean, I guess I could have separate loops, but then there'd be an awful lot of duplicated code -- everything except the conditionals. |
| 23:33 | <@EvilDarkLord> | Yes, that's what I mean. But I wouldn't go there, because it makes it look awful. |
| 23:35 | <@EvilDarkLord> | (Rather just rewrite as a C module if you need extra speed that much) |
| 23:35 | <&Derakon> | I'd really rather not do that because of the extra compiler step. :( |
| 23:35 | <&Derakon> | Cython at least can automatically compile at runtime. |
| 23:37 | <@EvilDarkLord> | What interpreter are you using? |
| 23:37 | < RichyB> | Derakon: I made an attempt at throwing the heat-map algorithm into C earlier but didn't get anywhere with it. |
| 23:38 | <&Derakon> | I note that fully-unrolling that dx/dy loop takes runtime from 2.394s to 1.713s in my speed test. |
| 23:38 | < RichyB> | Not sure whether the way in which I was trying to go about sharing buffers between C and Python is actually legal. |
| 23:38 | <&Derakon> | (With massive code duplication) |
| 23:38 | < RichyB> | EvilDarkLord: CPython, but I didn't see more than a 3x speedup at best with PyPy, and that only on certain sizes. |
| 23:38 | <@EvilDarkLord> | Derakon: Clearly you should have your cake and eat it too and dynamically generate the code and then call the interpreter on it. :P |
| 23:39 | <&Derakon> | Ugh! |
| 23:39 | <&Derakon> | Don't even joke about that. |
| 23:39 | <&Derakon> | I've dealt with code like that. >.< |
| 23:39 | < RichyB> | EvilDarkLord: Chameleon uses exactly that for HTML templating. |
| 23:39 | <&Derakon> | Mind, Cython might have a macro system I could use. |
| 23:42 | <&Derakon> | Oh wait, that speed gain was from optimizing the conditional tests. |
| 23:42 | <&Derakon> | As EDL suggested. |
| 23:44 | <@EvilDarkLord> | I'm assuming that almost all the time goes into lines 42+, is that correct? |
| 23:44 | <&Derakon> | Yeah. |
| 23:44 | <&Derakon> | Typically there's only one goal node. |
| 23:45 | <&Derakon> | But even in a moderately-constrained dungeon there can be thousands of iterations of the "while cellQueue" loop. |
| 23:57 | | * RichyB facepalm. |
| 23:57 | <@EvilDarkLord> | Derakon: Have you tried popping -1 instead of 0? |
| 23:57 | < RichyB> | I have a lot of off-by-one errors. |
| 23:57 | <@EvilDarkLord> | On line 43. |
| 23:57 | <&Derakon> | EDL: you mean, off the end of the list? Then it wouldn't be a breadth-first search. |
| 23:57 | <@EvilDarkLord> | Oh, derp |
| 23:58 | <@EvilDarkLord> | I just experimented and found that popping with -1 from a list of 100,000 entries deletes the list about 72 times faster than popping with 0. |
| 23:59 | <&Derakon> | Heh. |
| 23:59 | <&Derakon> | Yeah, because Python has to periodically move the list around in memory if you keep removing the head, IIRC. |
| 23:59 | <&Derakon> | Or something like that. |
| --- Log closed Sun Apr 21 00:00:35 2013 |