3 ms·

Nothing C does is even remotely special anymore. If anything it's total crap by modern standards because it makes performant abstractions harder. C code uses a

• jstimpfle 5y ago
  > C code uses a lot of linked lists because linked lists are easy. Strong disagree. I don't see any reason why a competent programmer would hand-code a linked list, which is more of a hassle to make than a simple array (e.g. using buffer pointer + capacity and/or length field), unless the linked list makes actual sense for performance.
  • mhh__ 5y ago
    I'm not saying you're duty bound to do it but rather giving an example of something which in my experience is encouraged by C since it's the path of least friction. Try writing a type that can automatically switch layout from AOS to SOA in C, you just can't do it.
    • uluyol 5y ago
      Out of curiosity, what are some languages that can automatically switch layout between struct-of-arrays and array-of-structs?
      • mhh__ 5y ago
        The only language I know for sure to do it for you (as in you don't have to write the type) was Jai a while back (I'm told Blow removed that feature). The only language I've actually done it in, is D. It's probably doable in many other nu-C languages these days, but D at very least can make it basically seamless as long as you do some try-and-break-shit testing to make sure nothing is relying on saving pointers when they shouldn't. This obviously constrains the definition of automatic ;) I don't have my implementation to hand because it grew out of patch that failed due to aforementioned pointer-saving in code that I'm not paid enough to refactor (), but here's one someone else made https://github.com/nordlow/phobos-next/blob/master/src/nxt/soa_petar_kirov.d https://github.com/nordlow/phobos-next/blob/master/src/nxt/s... there's another one in that repository too. I've never used those particular implementations but they're both by people I know so hopefully they're not too bad. A more subtle thing, which I haven't used in anger, but would like to try at some point is to use programmer annotations (probably in the form of user defined attributes) to try and group things so things are stored such that temporal locality <=> spacial locality, but I've never bothered to actually do it. There are some arrays of structs in an old bit of the D compiler that are roughly the size of a cacheline, and aren't accessed particularly uniformly. I profiled this and found that something like 75% of all LLC misses (hitting DRAM) were due to 2 particularly miserable lines... inside an O(n^2) algorithm.
      • wahern 5y ago
        ISPC has some support for this using the "soa<>" qualifier. For example, struct Point { float x, y, z; }; soa<8> Point pts[...]; for (int i = 0; i < 8; ++i) { pts[i].x + pts[i].y } behaves as if originally written like struct Point { float x[8], y[8], z[8]; }; Point pts; for (int i = 0; i < 8; ++i) { pts.x[i] + pts.y[i]; } See https://ispc.github.io/ispc.html#structure-of-array-types https://ispc.github.io/ispc.html#structure-of-array-types I've not yet had an excuse to use ISPC myself, unfortunately :(
      • dangets 5y ago
        Zig has a compile time annotation that can do it. https://zig.news/kristoff/struct-of-arrays-soa-in-zig-easy-in-userland-40m0 https://zig.news/kristoff/struct-of-arrays-soa-in-zig-easy-i...
      • tjalfi 5y ago
        Jovial 73 has the PAR qualifier which converts an AoS to a SoA.
    • jstimpfle 5y ago
      You can't hide AOS vs SOA in C and in most other languages, but that has nothing to do at all with linked lists. (you could use a macro to encapsulate the layout though, or in C++ could code a function that returns a reference) In what situations are linked lists the path of least friction??
      • mhh__ 5y ago
        I picked linked lists as a real example of something I've seen people do. It doesn't really make any difference my point. C is a bad programming language in 2022
        • jstimpfle 5y ago
          Well picking an invalid example (C encourages the use of linked lists in situations where they aren't a good idea) and a very questionable example (automatic conversions between different SAO/AOS representations are not mostly at an experimental stage but are an important feature for performance programming in 2022) is not a good way to support a claim that isn't empirically evident.
          • mhh__ 5y ago
            It's empirically evident in that no-one is picking C for new projects anymore. Anything fast is in C++ or C++ like languages.
• rixed 5y ago
  > C isn't the Lingua Franca of fast software anymore. What is it, then? > The reason why C programs can sometimes be faster, today, however is not an intrinsic property of the language but rather its inability to allow incompetent programmers to hide their bad data structures. I'm not sure I manage to parse that properly. What's wrong about not being able to hide bad data structures? And how is this making C faster?
  • pjmlp 5y ago
    C++ naturally.
    • urthor 5y ago
      Increasingly less so over time I presume. Sneering at C++ is rapidly overtaking insulting Javascript as the world's conversational standby.
      • pjmlp 5y ago
        “There are only two kinds of languages: the ones people complain about and the ones nobody uses.”
      • otabdeveloper4 5y ago
        Sour grapes.
• pjmlp 5y ago
  It never was.