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Re: qsort() vs. std::sort

Cross-posted to 2 groups.

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In comp.lang.c++ William Ahern <william@25thandclement.com> wrote:
> Unsurprising that inlining can improve performance.

The performance boost doesn't come from inlining. One single function call
wouldn't make a difference when it comes to sorting. It doesn't matter if
the std::sort() function gets inlined into the calling code or whether
the compiler decides to make it a separate function. That would only be
a difference of a few clock cycles at most.

The difference comes from what could perhaps be called "reverse inlining"
(which happens thanks to std::sort() being a template). In other words,
rather than std::sort() being embedded into the calling code, data from
the calling code gets embedded into the std::sort() implementation.
(In other words, we are doing the "inlining" kind of in reverse.)

This means that when std::sort() needs to, for example, compare two
elements, it knows exactly the type of the element and can do the
comparison "inlined" in its own code, rather than having to call some
external function provided by the caller.

> Your raw numbers are
> useless, though, as you're comparing different algorithms (C++ header
> template vs libc)

That's not a difference in algorithm. That's a difference in implementation.
For all we know std::sort() and qsort() could both use the exact same
sorting algorithm.

Note that making std::sort() a template isn't done primarily because it
makes it more efficient (it's a really nice bonus, but it's not the primary
reason why it's done). The main reason why it's a template is because
swapping elements in C++ may not always be possible by merely swapping
the underlying bytes of those elements. In other words, the swapping
is type-dependent. Achieving this is easiest with a template.

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qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-23 09:15 +0200
  Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-23 09:31 +0200
  Re: qsort() vs. std::sort Juha Nieminen <nospam@thanks.invalid> - 2022-04-25 05:56 +0000
    Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-25 08:27 +0200
  Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-25 01:16 -0700
    Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-25 12:59 +0200
      Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-25 13:32 +0200
        Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-25 05:26 -0700
          Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-25 17:41 +0200
            Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-26 00:46 -0700
              Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-26 12:19 +0200
      Re: qsort() vs. std::sort Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-25 05:24 -0700
        Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-25 17:42 +0200
    Re: qsort() vs. std::sort Juha Nieminen <nospam@thanks.invalid> - 2022-04-26 05:26 +0000
      Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-26 00:19 -0700
      Re: qsort() vs. std::sort scott@slp53.sl.home (Scott Lurndal) - 2022-04-26 14:03 +0000
        Re: qsort() vs. std::sort Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-26 08:50 -0700
        Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-29 01:38 -0700
          Re: qsort() vs. std::sort Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2022-04-29 02:39 -0700
            Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-29 04:06 -0700
    Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-26 12:28 +0200
      Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-26 04:54 -0700
        Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-26 14:10 +0200
          Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-26 06:23 -0700
            Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-26 16:26 +0200
  Re: qsort() vs. std::sort William Ahern <william@25thandClement.com> - 2022-04-27 17:03 -0700
    Re: qsort() vs. std::sort Bonita Montero <Bonita.Montero@gmail.com> - 2022-04-28 06:58 +0200
    Re: qsort() vs. std::sort Juha Nieminen <nospam@thanks.invalid> - 2022-04-28 06:33 +0000
      Re: qsort() vs. std::sort Öö Tiib <ootiib@hot.ee> - 2022-04-28 01:08 -0700
        Re: qsort() vs. std::sort Juha Nieminen <nospam@thanks.invalid> - 2022-04-28 08:23 +0000
      Re: qsort() vs. std::sort William Ahern <william@25thandClement.com> - 2022-04-28 02:55 -0700

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