• corroded@lemmy.world
    34·
    2 years ago

    I have the utmost respect for the ffmpeg developers; writing ASM is a skill I do not possess. I do have to wonder, though, would it be easier for cross-platform compatibility to write in C instead. I have always understood that C generally compiles almost directly to assembly with little to no abstraction overhead, and it would not require platform-specific ASM code. What is the logic in choosing ASM over C? I have no doubt there is a good reason.

    • Kushan@lemmy.worldEnglish
      241·
      2 years ago

      In 99 cases out of 100, you won’t be able to hand craft assembly better than a good compiler can - partly due to compilers being much better and partly due to the skill level required. 20 or 30 years ago compilers weren’t as good and a reasonably competent person could craft more optimised assembly but these days compilers are pretty damn good and you need some extra level of ability to best the compiler.

      However, there’s still that 1 time out of 100 and given how resource intensive ffmpeg is, it’s worth spending that extra time to hyper optimise the code because it’ll pay off massively.

    • stifle867@programming.dev
      14·
      2 years ago

      The logic is that it’s much faster which is important for code that runs on a large portion of the world’s devices. Pretty much anything to do with video is using ffmpeg. From a set top box, to your phone, computer, YouTube & Netflix, even on Mars.

      Video processing is hard, and when you’re processing that much data a x10 speedup is huge. That’s why it’s written in assembly. And there’s really no downsides to it because the original implementation is in C (cross-platform), then there are handmade assembly versions for each specific platform (performance). Win-win.

      • Heratiki@lemmy.mlEnglish
        8·
        2 years ago

        Not to mention size. Assembly is so incredibly small without all the code interpretation and library overhead. I remember some of the old warez scene exe’s for DOS that were a few kilobytes but ended up being a huge video quality intro. Some lasting minutes. Rather than a few seconds.

        • intelati@programming.dev
          71·
          2 years ago

          Assembly is probably the closest thing to magic humans have ever created.

          (I’m disqualifying String/Quantum as they are “theories” and not in common use)

      • ElectricCattleman@lemmy.worldEnglish
        1·
        2 years ago

        Great reads! Thanks for posting.

        I think it would be neat if, as something gained popularity, more and more of it were re-written in optimized assembly. I mainly work in .NET, which performs fine for what it is, but there are some libraries like Dapper (which is a micro-ORM) which are written in IL, which is incredibly difficult to do but results in it being insanely fast compared to what you could do in purely managed .NET. I’m sure if it were written in assembly it would be an order of magnitude faster than that.

    • ttmrichter@lemmy.world
      1·
      2 years ago

      I have always understood that C generally compiles almost directly to assembly with little to no abstraction overhead, and it would not require platform-specific ASM code.

      You have always understood incorrectly then. I’d recommend a trip over to Godbolt and take a look at the assembler output from C code. Play around with compiler options and see the (often MASSIVE!) changes. That alone should tell you that it doesn’t compile “almost directly to assembly”.

      But then note something different. Count the different instructions used by the C compiler. Then look at the number of instructions available in an average CISC processor. Huge swaths of the instruction set, especially the more esoteric, but performance-oriented instructions for very specific use cases, are typically not touched by the compiler.

      In the very, very, very ancient days of C the C compiler compiled almost directly to assembly. Specifically PDP-11 assembly. And any processor that was similar to the PDP-11 had similar mappings available. This hasn’t been the case, however, likely longer than you’ve been alive.