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Re: Boost.bind and performance penalties?

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On 05/25/2011 01:56 PM, Rune Allnor wrote:
> Hi all.
[snip]
> The point is that I can't afford much run-time overhead, or
> it will signifigantly impact the application.
>
> Now, there are several variants of computations that I can
> do on the data x. I'd like to use function objects or pointers
> to specify how to do the computations, and am thinking of
> using boost.bind to declare these function pointers when
> calling this library.
>
> What run-time overheads, if any, would be expected when
> using function pointers, as opposed to 'hard-wiring' the
> computations inside the library?

I guess it depends on how complicated the functions are, in two ways.

One: if they take long time, the call overhead is _relatively_ small.

Two: how complicated they are, impacting optimizing possibilities. E.g. 
simple multiplication can be SSE'd ('vectorized') if inline'd or 
deducted by compiler in some other way. Such optimisations cannot be 
done - in most cases - when the call is indirect enough that the 
compiler cannot be sure it knows the called function body. This can be 
significant.

In general bind() is not light, and even function pointers, or even 
worse pointers to members, should not be called in a tight loop, if only 
for the call itself, let alone missed optimisations.

These are mostly rules of thumb. If you have a lot of time to spend on 
programming, use expression templates, or inline at least. If you 
cannot, use boost::bind and just don't worry.

HTH
Edek

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Thread

Boost.bind and performance penalties? Rune Allnor <allnor@tele.ntnu.no> - 2011-05-25 04:56 -0700
  Re: Boost.bind and performance penalties? Edek <edek.pieITAKNIECZYTAM@gmail.com> - 2011-05-25 16:45 +0200
    Re: Boost.bind and performance penalties? Rune Allnor <allnor@tele.ntnu.no> - 2011-05-25 21:35 -0700
      Re: Boost.bind and performance penalties? Edek <edek.pieITAKNIECZYTAM@gmail.com> - 2011-05-26 11:34 +0200
        Re: Boost.bind and performance penalties? Rune Allnor <allnor@tele.ntnu.no> - 2011-05-26 02:40 -0700
          Re: Boost.bind and performance penalties? Edek <edek.pieITAKNIECZYTAM@gmail.com> - 2011-05-26 12:53 +0200
            Re: Boost.bind and performance penalties? Rune Allnor <allnor@tele.ntnu.no> - 2011-05-26 04:19 -0700
              Re: Boost.bind and performance penalties? Jeff Flinn <TriumphSprint2000@hotmail.com> - 2011-05-26 16:11 -0400

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