foxhill · HackerTrans

foxhill

1,288 karmajoined 15 tahun yang lalu

Submissions

Trust your compiler: Modern C++

categorica.io

68 pointsby foxhill27 hari yang lalu45 comments

Implementing UFCS for C++ in Clang

dancrn.com

51 pointsby foxhill6 tahun yang lalu23 comments

Show HN: Shade – a quick-and-dirty glsl prototyping tool

github.com

25 pointsby foxhill8 tahun yang lalu1 comments

MtGox account database leaked

forum.bitcoin.org

106 pointsby foxhill15 tahun yang lalu101 comments

comments

12 hari yang laludiscuss

i do wonder how something like this can be generally implemented. i presume this must only support a subset of SQL/plpgsql, as some things would be.. utterly insane to manage manually. e.g., if i have a table with a btree-gist overlap constraint, or some inclusion-exclusion check-constraint (or literally any constraint that requires multiple rows to be fully determined - there are quite a lot of them), how on earth does this work?

there's a reason why postgres writing is (mostly) serialised (asterisk) to a single writer (asterisk asterisk). something something ACID, but in short by having multiple writers improves availability, but weakens integrity.

22 hari yang laludiscuss

that's a nice example. on my M4, i measured 3.4s vs. 0.42s. honestly surprised there's ~10x improvement to be found.

as you've pointed out, you've literally micro-optimised this - isn't this what you'd expect? :)

tahun laludiscuss

it probably shouldn’t be a “release” thing. actually, certainly. i do wonder how many bugs would never have seen the light of day, if someone’s “set” actually turned out to be a sequence (i.e. allowed duplicate values) resulting in a debug build raising an assert.

tahun laludiscuss

huh. very cute. in the past, i had an idea for terser lambda syntax, similar to C#'s expression body functions - which i did end up implementing in clang:

    auto sum = [](auto a, auto b): a+b;

but this is something else. i didn't think i'd like it at first, but actually i think i might be coming around to it. the.. dollar syntax is regrettable, although it's not a show stopper.

tahun laludiscuss

you can't be serious, surely?

yes, mozilla's TOS update is a bad thing, but switching to chrome (or chromium-based) for it is really cutting your nose to spite your face.

2 tahun yang laludiscuss

you’re conflating reaction times and latency perception. these are not the same. humans can tell the difference down to 10ms, perhaps lower.

if you added 200ms latency to your mouse inputs, you’d throw your computer out the of the window pretty quickly.

2 tahun yang laludiscuss

what a miss.

i’d consider myself a day-to-day c++ engineer. well, because i am. i like lots of things from rust. there’s a few things i don’t. c++ has a lot to learn from rust, if it is to continue to exist.

but really.. isn’t this the point of the language? you need to understand the borrow checker because.. that’s why it’s here?

maybe i’m missing something.

2 tahun yang laludiscuss

friends. you understand that you can just.. take it off, right?

fully unscrew the cap then just either continue twisting the cap over the the edge - honestly effortless - or just.. pull it off? the cap still functions as a cap, afterward.

apologies, but i don’t understand the furore over this change.

2 tahun yang laludiscuss

so, when do you want to die, then?

really, i’m not trying to be mean here. you assert life must be finite, and all i’m asking is how finite it should be.

2 tahun yang laludiscuss

apologies, i wasn't being specific; none of what i said necessitates a CRT display, it was only as an example of how an older technology had less latency.

if modern a modern 60Hz LCD/OLED display couldn't get beneath 16.6ms latency, then what exactly is tearing?

2 tahun yang laludiscuss

you don't need to "beam race" to achieve sub-frame latency - you don't need to be accurate. switching off vsync should, principally, be enough to achieve this.

otherwise, yes, modern APIs go out of their way to avoid the possibility of this (the dreaded "tearing" artifacts you see from the frame buffer being changed during the transmission of the video signal to the monitor). i don't believe older techniques like you've mentioned are at all possible today, and only really made sense to talk about when analogue displays were the norm.

2 tahun yang laludiscuss

> An application with 10 frames of latency will be faster on a 1 kHz display than a perfectly coded application on a 60 Hz display.

thats actually not true. you seem to be implying that the best a 60hz display can manage is 16.6ms of latency. indeed that is the worst case value, but you should consider that early graphics technologies involved changing display modes mid scan.

it’s actually not ridiculous to suggest that old platforms had sub-millisecond latency; they did. if the scanline was on, or just before, the line where you would interact (i.e., the prompt line), the text you enter would appear immediately.

of course, “vsync”, tear free, and such like approaches “fixed” this - necessarily by adding at least a frame’s worth of latency - but also adding perceptual latency.

it’s an oft-overlooked aspect of refresh rates. a 60hz CRT, without vsync, still has the lower bound of latency lower than a 120hz display. perhaps even 240hz.

i’ve used two 240hz displays for years now. i’ll never go slower than that.

2 tahun yang laludiscuss

fair enough :) apologies!

2 tahun yang laludiscuss

correct me if i’m wrong, but i believe the point that is trying to be made is;

a system user/admin has an intuition about files. saying that ‘journalctl -f -u’ (fu, indeed :) and whatever else is inherently undiscoverable, and is a.. basically orthogonal mechanism for handling what should be a simple task. i.e., viewing some logs. it’s far easier to compose and extend from files (what if i only care about the mtime of the log, for instance), than this.

look, i think systemd isn’t.. terrible. i also think it’s suffered a bit of complexity fetishisation, and it seems as though that this resulting complexity may have become invisible to you.

run0 doesn’t seem like a bad idea. but i am wincing a bit at the thought of unrestricted javascript determining access control.

3 tahun yang laludiscuss

yes, that’s what collective health care means, regardless of if it’s state-mandated, or fully private.

you, or i, don’t get to decide what’s fair to treat, or who’s deserving of treatment.

3 tahun yang laludiscuss

the (presumably) stateless, serverless function that appears to serve the site has.. crashed?

i dunno, i feel like the wording of this error message could be improved :)

3 tahun yang laludiscuss

only if you want to store them in the open air. vacuum sealing them would obviate the need for an expensive hvac bill.

and deep ground is not ridiculous. we’re expecting the storage to be in the “mostly write only” regime, after all.

3 tahun yang laludiscuss

i am quite familiar with compiler internals :)

of course, across the TU boundary things get difficult, but i don’t think it’s fair to dismiss LTO entirely (although.. i agree with the thesis that it’s not particularly.. good)

similarly, de-virtualisation is an optimisation technique compilers will aggressively use to improve performance, although you’re right that it can’t look through another source file, so it is not without limitations here.

but we’re not being general, we’re being specific; the safety issues that are being discussed are well within the remit of the c++ type system here, and i don’t think we’re doing any favours to anyone by letting this rvalue be accessed in this way. it is certainly not idiomatic to provide library code that can so violently implode with seemingly regular use. i find it difficult to believe that lifetime issues like this are undiagnosable.

3 tahun yang laludiscuss

ah, sorry, i didn’t read that correctly.

perhaps for values like this you’re fine. i think my point still stands about the reader of a built-in list/sequence type, surely?

and, not to sound facetious, that’s exactly what optimisers do :)

the c++ type system is more than capable about reasoning about lifetimes, the issue is that, with c++, it’s an optional part of the language. also, the lack of non-destructive moves. but to require both of those things in the language would require, essentially, the borrow checker in rust.

3 tahun yang laludiscuss

i could be wrong, but i’m reasonably confident that this is UB for even trivial types? someone more knowledgeable with the language lawyering would need to opine one way or the other.

regardless of that outcome, i think i’d prefer to require a value preserving the lifetime of the reader/view. in the cases that it may not be necessary, i'd prefer to lean on the optimiser to take care of it..!