4 ms·

> I'd say that printf, with its own DSL, is actually pretty slow. Yes, of course it is. That's why I took it as an example. Since I work on RealTime systems I

by deng 8y ago

> I'd say that printf, with its own DSL, is actually pretty slow. Yes, of course it is. That's why I took it as an example. Since I work on RealTime systems I usually have to use plain 'write' instead. But that is because 'printf' is an incredibly complex function, not because 'C is slow'.

simias 8y ago
At this point I feel like it's almost a philosophical argument but: - printf is a standard function in C's stdlib. - Because of the nature of the function (using a special purpose format strings and varargs instead of some kind of generic system) the function can't really be aggressively optimized and inlined without compiler magic. This limitation is caused by C's own limitations when it comes to generic programming and type introspection, printf needs to be told explicitly through a "side-channel" (the format string) what types to expect because C lacks the infrastructure to do that by itself. It also means that you can't extend the function for custom types and that you can't type-check the parameters without compiler magic. - Even though some compilers do implement special magic around printf to perform more aggressive optimizations (like replacing it with "puts" if there's no formatting going on for instance) it's still generally trivial to beat its performance in non-trivial case with handwritten code. Given all of the above I would say that makes this particular corner of C rather slow indeed. Or at least slower than it might be compared to an hypothetical language that made it easier to optimize string formatting.
- skrebbel 8y ago
  You're entirely right, but I feel like you're trying really hard to misunderstand deng's original comment. It's an apt analogy, partly because of what you wrote. This article's title is as ridiculous as an article titled "Is C fast?" with a story about a faster_printf that only supports %d.

by deng 8y ago

simias 8y ago

At this point I feel like it's almost a philosophical argument but: - printf is a standard function in C's stdlib. - Because of the nature of the function (using a special purpose format strings and varargs instead of some kind of generic system) the function can't really be aggressively optimized and inlined without compiler magic. This limitation is caused by C's own limitations when it comes to generic programming and type introspection, printf needs to be told explicitly through a "side-channel" (the format string) what types to expect because C lacks the infrastructure to do that by itself. It also means that you can't extend the function for custom types and that you can't type-check the parameters without compiler magic. - Even though some compilers do implement special magic around printf to perform more aggressive optimizations (like replacing it with "puts" if there's no formatting going on for instance) it's still generally trivial to beat its performance in non-trivial case with handwritten code. Given all of the above I would say that makes this particular corner of C rather slow indeed. Or at least slower than it might be compared to an hypothetical language that made it easier to optimize string formatting.

skrebbel 8y ago
You're entirely right, but I feel like you're trying really hard to misunderstand deng's original comment. It's an apt analogy, partly because of what you wrote. This article's title is as ridiculous as an article titled "Is C fast?" with a story about a faster_printf that only supports %d.