Beta
×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

Comments

top

Apple WWDC 2014: Tim Cook Unveils Yosemite

nneonneo Metal (411 comments)

One of the updates that folks seem to have overlooked is Metal, Apple's upcoming replacement for OpenGL.

While I think Apple is likely to continue supporting OpenGL for the foreseeable future, it's somewhat worrying that they've decided to just build a brand-new graphics library. It represents a refocusing of their optimization efforts, certainly, so in the future I would expect devs to have to use Metal in order to obtain decent graphics performance. This in turn will make development even harder, especially for cross-platform shops which expect OpenGL to work reasonably well in all environments...

about 4 months ago
top

Apple WWDC 2014: Tim Cook Unveils Yosemite

nneonneo Re:Falling through cases is quite useful at times (411 comments)

Defaults should be sane, and optimized for the common case. Fall-through-by-default is not the common case, it's the exceptional case. Because C chose fall-through-by-default, programmers are penalized for the much more common case of no-fall-through by having to type "break;" at the end of every frickin' case statement.

Because of this, common C practice is to annotate intentional fall-through statements with a comment, like so:

switch(expr) {
    case superset:
/* superset code ...*/
/* FALLTHROUGH */
    case base:
/* base code ...*/
}

So, guess what Swift does? That's right, an explicit fallthrough keyword, which you can apply to get the uncommon (but, as you noted, occasionally useful) fallthrough behaviour. This is both wonderfully self-documenting, and eliminates the need for break in the common case. Switch statements in Swift are shorter and safer as a result. (Also, their use of Lisp/Scheme/...-esque matching semantics for switch is a nice touch, as are the genericized Enums...but that's a story for later).

about 4 months ago
top

Python 3.4 Released

nneonneo Re:Not all C libraries release the GIL (196 comments)

Any C library can touch Python objects any time it likes, by nature of being linked to the Python C-API. However, you can only safely access Python objects while holding the GIL. CPython libraries are entered into with the GIL held (otherwise you couldn't even interact with the arguments given to the function), and they may decide to release the GIL some time later (and promise not to touch the Python API while the GIL is not held).

*Many* CPython release the GIL during operations that may be long-running, so you get the illusion that basically any long-running C operation releases the GIL.

PIL not releasing the GIL should be construed a bug in this case.

about 6 months ago
top

Book Review: Core Python Applications Programming, 3rd Ed.

nneonneo Re:Python is pretty decent, I only have two concer (65 comments)

If you're feeling *particularly* devious, you can use a little-known Python feature called "for-else" (also "while-else") which allows you to tag "else" clauses onto for loops. Such a clause executes only if the loop runs to completion 'naturally' (i.e. if no break or exception happens within the loop block).

As a relatively obscure language feature, using it might make your code harder to read. It can help make a multilevel break (chained "else: continue; break" snippets at the end of loops), and reduces the number of flag tests and sentinels you need to do (e.g. a linear search, wherein the "else" case simply contains the if-not-found logic).

There are other alternatives to multi-level break: exceptions can break out of any number of loops until they reach an appropriate handler block, and function returns can always break out of any loop up to the top of the function.

As for switch/case: In C, they were basically a thin wrapper around jump tables for most switches (e.g. enums, small integers, duff's device, etc.). Python's preferred alternatives are key-value dictionaries (hashtables) or if/elif cascades. The former is very easy to setup and manipulate in Python (e.g. {1: 'spam', 2: 'eggs', 3: 'ham'}), unlike in C or C++. The latter is far more flexible than switch/case (e.g. being able to test ranges of values with "A <= x <= B" queries, test for multiple values with "x in (A, B, C)", or do arbitrary tests like "x.isspace()"), while avoiding the complexity of an entirely new language construct.

Finally, goto exists in Python as a third-party module. Go ahead, try it: it really works!

more than 2 years ago
top

Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

nneonneo Re:Reminds me of an old RPS contest... (225 comments)

This implementation is not infeasible even when the players run in separate processes. I can observe your rand() state through the moves you make, and provided the remainder of the argument is the same (seeded with system time at the start of the match, simple RNG processing to derive a move), I can simply play randomly for the first 30 rounds (3^30 > 2^32) and observe your state. If I can come up with a set of RNG parameters (time-based seed, rand algorithm, sequence offset, processing strategy) that outputs your move sequence, then I can still beat your bot with a slightly worse win record. It takes 30 times more computational power, so about 180000 possibilities, but it's still tractable.

more than 2 years ago
top

Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

nneonneo Re:Reminds me of an old RPS contest... (225 comments)

Suck is relative. I was implying they sucked according to GP's definition, which was that a "good" algorithm would require lots of data & computation time to beat. I would agree that they don't suck for their intended purpose (simple, fast, reasonably random, repeatable numbers). However, rand() does get (mis)used in a lot of contexts (especially security-conscious ones, or applications vulnerable to algorithmic complexity attacks) where it should not be used.

I should mention, though, that even in cases where it "shouldn't" matter, a weak rand() enables attacks on systems that should otherwise behave randomly. For example, many games (as you mention) use very simple implementations of rand(); such simple implementations also allow particularly hard-core gamers to abuse the system and earn much higher rewards (stat boosts, attack rolls, random encounters, etc.) than they ought to. Heck, there's an entire subcommunity of Pokémon game players dedicated to beating the game (and/or outperforming their peers) through methodical, systematic RNG abuse.

more than 2 years ago
top

Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

nneonneo Re:Reminds me of an old RPS contest... (225 comments)

0) I have source code for my bot, the tourney announcement, and the tourney results. If you are really curious, ping me at my email address.

1) I never said you were *playing* a random opponent. Against an *arbitrary* opponent your optimal strategy is to play randomly. Any other strategy that you play can be exploited to your loss. In this way, random really is the game-theoretic optimal strategy. It's not just a buzzword.

2) Of course. I'm exploiting an implementation detail. This is a classic side-channel attack on an otherwise secure system.

3) Yes. I looked up the source code for libc implementations online. It's easy: google ' rand.c'. Examples: http://fxr.watson.org/fxr/source/stdlib/rand.c?v=FREEBSD-LIBC, http://fossies.org/dox/glibc-2.15/random_8c_source.html. I also got Microsoft's rand() implementation for their MSVC runtime because the source code for that comes with Visual Studio. Yes, I was using Windows. Contest submissions had to be in C or C++, and most programmers would rather use rand() (portable, simple, easy) than implement their own random() function or use the less-portable /dev/[u]random.

4) Contest programs ran in the same process, so your rand() state was shared. srand was forbidden, but we were given the tournament engine source code and so we knew when srand() was called and with what arguments (time(NULL)). To be specific: I pulled a single rand() value, then ran all my implementations of rand() with different seeds in the neighbourhood of time(NULL), and ran them for a variable number of iterations (up to 20, I think) to guess the sequence offset. The processing strategy was simply observing what values they were adding to the rand() value before taking it mod 3. The input is about 20 seconds * 5 libcs * 20 sequence offsets * 3 "processing strategies" = 6000 possibilities. Four dimensions, but they can all be constrained to small values.

more than 2 years ago
top

Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

nneonneo Re:Reminds me of an old RPS contest... (225 comments)

I took first place in the full round-robin. The second part of the contest was a knockout tournament, and I wasn't using the kind of super-sophisticated modelling that my opponents used since the RNG breaker was already a fair amount of work. Consequently, at best I tied strong opponents, and lost on time.

more than 2 years ago
top

Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

nneonneo Re:Reminds me of an old RPS contest... (225 comments)

Yes indeed, neonbot was my entry. Quite a remarkable small world. The contest was in 2007 (my first year of undergrad), and it was probably my favorite event of the year. Thanks for judging!

more than 2 years ago
top

Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

nneonneo Re:Reminds me of an old RPS contest... (225 comments)

I'd think that unless you were playing a very large number of rounds such that you could infer the opponent's PRNG function and seed, or unless the opponent PRNG was REALLY bad, this would not work.

Actually, supposing the seed state is 32 bits in size, it really doesn't take that many rounds. Each round, one of three outcomes is produced. This yields roughly 1.6 bits of information about the generator's internal state. After 20 rounds, you have, in theory, enough information to infer the PRNG seed. If you can predict the opponent's move for 30 straight rounds, you can be pretty confident that you've determined both the seed and the function precisely. This works for arbitrary seeds.

Maybe if the seed were the time to the nearest hour you might be OK. However, if it used time to a millisecond then you'd have almost no chance of success. Any decent PRNG will show what would appear to be completely different behavior with even a slightly different seed.

With regards to the timestamp: srand(time(NULL)) isn't a random seed. If you can guess when the process called this function (hint: it's at least after the process was started!), you can then bruteforce over a very small number of possibilities. If the process was started, say, at 7:00pm for the contest start, and you run at 8:30pm, you've got a search space of just 5000000 milliseconds, which is trivial. My implementation worked for this contest (as evidenced by its extremely high win rate against rand()-using bots).

Now, if the PRNG were really lousy maybe you'd have a shot. It just seems unlikely that such a function would exist in any well-used library since the 60s. Sure, lots of functions are inadequate for cryptography, but even defeating these poor algorithms usually requires lots of data collection and a huge search. A PRNG that takes 5 years of supercomputer time would be considered broken, since a brute force keysearch might require the age of the universe. That doesn't mean that you're going to defeat it with a few rounds of RPS to figure out what it is doing.

This PRNG-breaking approach would work equally well for a crappy linear-congruential generator as for a modern Mersenne Twister, since it relies only on being able to guess the seed (not the entire internal state).

Most libc implementations of rand() really suck. They were originally implemented for memory economy and speed, and there was no concern about security. Now, such implementations are largely retained for compatibility, so that older programs can still produce the same results using fixed seeds. The various libcs are, arguably, the most-used libraries in existence. To beat many of these generators requires just one (or two) observations of the full 32-bit output, plus a trivial amount of computation.

more than 2 years ago
top

Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

nneonneo Re:Reminds me of an old RPS contest... (225 comments)

Maybe about 10% or so. The contest was five years ago, so some of the details are a bit fuzzy. I don't believe we ever got the source code for other competitors, either, so I wouldn't know if they were using an RNG strategy or just a simple predictable one.

more than 2 years ago
top

Fundamentalist Schools Using "Nessie" To Disprove Evolution

nneonneo Re:Was Jesus riding Nessie? (936 comments)

Evolution doesn't need to "progress" quickly. It has no defined end-goal, only the continued adaptation of species. Life adapts to its environment, whether the environment is an asteroid crater or an industrial park.

Evolution doesn't have to be "induced" by any great event. Catastrophic events are just one way in which evolution can operate, since they produce ecological voids which are rapidly filled by new (adapted) flora and fauna. Regular adaptation to ever-changing natural (and artificial) environments also drives evolution.

more than 2 years ago
top

Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

nneonneo Reminds me of an old RPS contest... (225 comments)

I once participated in a Rock-Paper-Scissors tournament put on by Epson (see, for example, http://www.campuslogix.com/rps_challenge/rps_challenge.html). They basically said "write a bot that will play RPS". Of course, the game-theoretic optimal strategy in such a contest is to just play randomly. You can beat the (Epson-supplied) rockbots and rotatebots easily, so with a bit of work you can do slightly above average.

Seeking a greater advantage, though, I coded my bot to also include a set of predictors for the random number generators for several popular libcs (as I did not which OS or distro the tournament machine would use). During a round, I would guess the random seed (current system time +/- a few seconds), the sequence offset, RNG processing strategy, and the algorithm used, and simply run a parallel copy of the libc RNG used by my opponent.

I was therefore able to beat most RNG-using opponents 9998/10000 times easily, a finding which rather surprised the judges :) I didn't win top prize (algorithm wasn't fast enough, and it turns out that was weighted more heavily than I expected), but I did get a high ranking and a cash prize.

Goes to show: sometimes a bit of "cheating" works well.

more than 2 years ago
top

Rockstar Creates 'Cheaters Pool' For Game Hackers

nneonneo AI Challenge (228 comments)

They've (either purposefully or inadvertently) created for themselves a bit of an AI challenge. If the hackers take this seriously enough, we could see the development of some pretty advanced game-specific AIs.

And, just like Australia, they might all eventually come to be accepted as mostly-normal members of society.

more than 2 years ago
top

Kernel.org Compromised

nneonneo Re:he's talking about tarballs (312 comments)

...two months is all you need to cross from one year to the next, which, under the %m-%d-%Y scheme, would still fail to sort in the expected chronological order.

about 3 years ago
top

Kernel.org Compromised

nneonneo Re:he's talking about tarballs (312 comments)

Need I point out that %Y-%m-%d sorts properly, whereas %m-%d-%Y does not? When's the last time you needed releases sorted by month but not year?

more than 3 years ago
top

IE6 Still Going Strong In China

nneonneo Re:Aye, pirates be the reason IE6 just won’t (158 comments)

I once repaired a computer with no fewer than 250,000 copies of a particular virus (don't recall which) installed. With each virus .exe weighing in at 12KB, that was 3GB of virus code on the laptop (given that this was about 6 years ago, that was a substantial amount of space).

The machine was a new laptop with XP SP1 installed (so no firewall). On its first day, it was connected to a university LAN for 8 hours non-stop, while a virus was running around the network. The virus did not have code to detect an existing infection, so it simply reinfected the machine many times.

It ran fine until the owner shut it down. Upon restarting, every virus .exe tried to start, resulting in a hung system on boot. It took a commercial antivirus program over 10 hours to finish clearing the machine.

more than 3 years ago
top

Creator of China's Great Firewall Pelted With Shoes

nneonneo Re:Unfortunate... (220 comments)

The soap box is censored, the ballot box is a sham, and the jury box is rigged. Maybe then you see why some would resort to force?

more than 3 years ago
top

Is Apple Turning Into the Next "Evil Empire"?

nneonneo Re:Yes and no (722 comments)

I didn't realize using a standard audio format, with tons of support from tons of software and hardware, and with better licensing terms than MP3 counted as "lock in".

You are also drawing an unfair comparison between Microsoft's desktop operating environment and Apple's mobile environment. Apple runs iOS like basically any game console; if you think that iOS is evil, then you probably also think Nintendo is evil too for making their platforms locked down.

On the other hand, Apple's Mac OS X operating system is far more open than Microsoft's ever was. On OS X, the kernel (Darwin) is open-source, the browser (WebKit) is open-source, the compiler (LLVM/Clang) is open-source, and the company employs developers who maintain and contribute back to these projects.

Apple also sits on several standards committees, and actively participates in standards development and promulgation.

In many, many ways, Apple is not nearly as "evil" as you seem to think.

more than 3 years ago

Submissions

nneonneo hasn't submitted any stories.

Journals

nneonneo has no journal entries.

Slashdot Login

Need an Account?

Forgot your password?