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Comment: Metal (Score 3, Interesting) 411

by nneonneo (#47152395) Attached to: Apple WWDC 2014: Tim Cook Unveils Yosemite

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...

Comment: Re:Falling through cases is quite useful at times (Score 1) 411

by nneonneo (#47152345) Attached to: Apple WWDC 2014: Tim Cook Unveils Yosemite

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).

Comment: Re:Not all C libraries release the GIL (Score 1) 196

by nneonneo (#46527037) Attached to: Python 3.4 Released

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.

Programming

+ - CMU Researcher Creates an Acoustic QR Code->

Submitted by Hesh
Hesh (449135) writes ""Robert Xiao at CMU has created an acoustic equivalent of a QR code, by patterning notches into materials like plastic, glass, and stone. They are lower resolution, but could be much smaller and overall less invasive. " You can find out more details here: http://hackaday.com/2012/10/11/acoustic-barcodes-deliver-data-with-a-fingernail-and-microphone/ and see a video of it in action here: http://www.youtube.com/watch?v=NB_UoJGd5-E"
Link to Original Source
Iphone

+ - SNL skewers reviewers/tech journalists in iPhone 5 skit->

Submitted by alphadogg
alphadogg (971356) writes "Saturday Night Live this weekend skewered tech journalists’ for their whining about iPhone 5 shortcomings, with a skit featuring a trio of Chinese factory workers answering their critics and besting them. The skit, featuring guest star Christina Applegate as host of the Tech Talk show, examines the Apple iPhone 5’s “plethora of glitches and design flaws” with a panel of tech journalists from Cnet, Gizmodo and Wired. The host then brings on three “peasant workers” from the Chinese factory where the iPhone 5 was built in an effort to put the journalists’ complaints into broader perspective. Hilarity ensues...."
Link to Original Source
China

+ - The China Question->

Submitted by
CowboyRobot
CowboyRobot writes "Last week the U.S. Congress recommended that Chinese firms Huawei and ZTE should be barred from the U.S. in the name of domestic cyber security. The proposed threat is that Chinese-made hardware may contain "Manchurian candidate" spyware that could allow the People's Liberation Army to get access to sensitive networks in the U.S., Europe, and elsewhere. Politicians will debate the effect on trade that this threat could cause, but what can network managers do about it? But what does that mean for everyone else? Remember that malware "can be seeded in infrastructure such as switches, servers and routers before they're ever turned over to a customer. Also, you should not have blind faith in your vendor, who may be if not malicious, at least ignorant of security issues. And remember that suspicion and vigilance are not the same thing, nor exclusive of each other."
Link to Original Source

Comment: Re:Python is pretty decent, I only have two concer (Score 2) 65

by nneonneo (#40825815) Attached to: Book Review: Core Python Applications Programming, 3rd Ed.

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!

Comment: Re:Reminds me of an old RPS contest... (Score 1) 225

by nneonneo (#40475521) Attached to: Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

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.

Comment: Re:Reminds me of an old RPS contest... (Score 1) 225

by nneonneo (#40475503) Attached to: Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

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.

Comment: Re:Reminds me of an old RPS contest... (Score 2) 225

by nneonneo (#40472921) Attached to: Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

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.

Comment: Re:Reminds me of an old RPS contest... (Score 1) 225

by nneonneo (#40472733) Attached to: Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

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.

Comment: Re:Reminds me of an old RPS contest... (Score 1) 225

by nneonneo (#40472653) Attached to: Robot Hand Beats You At Rock, Paper, Scissors 100% of the Time

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.

The number of arguments is unimportant unless some of them are correct. -- Ralph Hartley

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