Re: What practice can get speed improvement in C++?

From	"Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>
Newsgroups	comp.lang.c++
Subject	Re: What practice can get speed improvement in C++?
Date	2015-07-15 05:07 +0200
Organization	A noiseless patient Spider
Message-ID	<mo4ima$1e2$1@dont-email.me> (permalink)
References	<aaa4556e-8239-412c-be9d-7308a1a2cbb6@googlegroups.com>

Show all headers | View raw

On 15-Jul-15 1:53 AM, fl wrote:
>
> I am given the following question:
>
> Experience in C/C++ code optimization for speed improvement.

I read that as, "list your experience with speed optimization for C and 
C++ code".

> I can only get the following answers:
>
> 1. Use reference to replace a direct parameter in function call;
> 2. Use register for some frequent variables;
> 3. Use assembly code to replace C code
> 4. Unroll a loop(?)
>
> What is your opinion to the question?

First, it's about particular programming languages, so presumably if you 
have experience with MEASURING, which is the most important thing, then 
you are expected to relate something of how you did that differently for 
the two mentioned languages, than for some other possible languages. I 
think you would be expected to mention some common tools and approaches 
for this, such as profiler, Unix-land `time` command, instrumenting code 
with timers and logging, and just dead reckoning (which can tell you if 
other ways are necessary). Regarding timers it would be nice if you know 
about the very limited resolution of C library time in Windows, and 
knowing about higher resolution C++11 timers, and about Boost timers.

Second, after measuring comes algorithmic considerations. Replacing an 
O(n^2) algorithm with an O(n) algorithm is common. E.g. I think it would 
count in a positive way if you mentioned how you once optimized some 
repeated string concatenation, perhaps in Java. Knowing about support 
for this in C++11 would be extra point.

Third, simple mechanical optimizations like you mention above. But your 
point (2), "Use register for some frequent variables", would count 
NEGATIVELY if I were to evaluate the answer, unless this is about an 
application to become part of a compiler development team (for ordinary 
app code you should leave that to the compiler: forcing it you're likely 
to do worse). On the other hand, knowing that the "register" keyword was 
deprecated in C++11 would be positive.

Cheers & hth.,

- Alf

-- 
Using Thunderbird as Usenet client, Eternal September as NNTP server.

Thread

What practice can get speed improvement in C++? fl <rxjwg98@gmail.com> - 2015-07-14 16:53 -0700
  Re: What practice can get speed improvement in C++? Barry Schwarz <schwarzb@dqel.com> - 2015-07-14 17:23 -0700
    Re: What practice can get speed improvement in C++? bartekltg <bartekltg@gmail.com> - 2015-07-15 15:10 +0200
      Re: What practice can get speed improvement in C++? JiiPee <no@notvalid.com> - 2015-07-16 05:00 +0100
        Re: What practice can get speed improvement in C++? Öö Tiib <ootiib@hot.ee> - 2015-07-16 01:04 -0700
          Re: What practice can get speed improvement in C++? JiiPee <no@notvalid.com> - 2015-07-16 16:48 +0100
            Re: What practice can get speed improvement in C++? JiiPee <no@notvalid.com> - 2015-07-16 16:52 +0100
        Re: What practice can get speed improvement in C++? bartekltg <bartekltg@gmail.com> - 2015-07-16 13:23 +0200
          Re: What practice can get speed improvement in C++? Öö Tiib <ootiib@hot.ee> - 2015-07-16 06:54 -0700
            Re: What practice can get speed improvement in C++? bartekltg <bartekltg@gmail.com> - 2015-07-16 17:30 +0200
              Re: What practice can get speed improvement in C++? Öö Tiib <ootiib@hot.ee> - 2015-07-16 11:16 -0700
                Re: What practice can get speed improvement in C++? bartekltg <bartekltg@gmail.com> - 2015-07-17 17:06 +0200
          Re: What practice can get speed improvement in C++? JiiPee <no@notvalid.com> - 2015-08-04 16:14 +0100
  Re: What practice can get speed improvement in C++? Victor Bazarov <v.bazarov@comcast.invalid> - 2015-07-14 20:29 -0400
    Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-07-14 19:50 -0700
  Re: What practice can get speed improvement in C++? "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2015-07-15 05:07 +0200
  Re: What practice can get speed improvement in C++? Lőrinczy Zsigmond <nospam@for.me> - 2015-07-15 06:38 +0200
  Re: What practice can get speed improvement in C++? Paavo Helde <myfirstname@osa.pri.ee> - 2015-07-15 00:22 -0500
    Re: What practice can get speed improvement in C++? fl <rxjwg98@gmail.com> - 2015-07-16 04:34 -0700
      Re: What practice can get speed improvement in C++? Martijn van Buul <pino@dohd.org> - 2015-07-21 09:28 +0000
  Re: What practice can get speed improvement in C++? Juha Nieminen <nospam@thanks.invalid> - 2015-08-03 08:16 +0000
    Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-08-03 13:48 -0700
      Re: What practice can get speed improvement in C++? Juha Nieminen <nospam@thanks.invalid> - 2015-08-04 08:21 +0000
        Re: What practice can get speed improvement in C++? Öö Tiib <ootiib@hot.ee> - 2015-08-04 08:07 -0700
        Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-08-04 10:15 -0700
          Re: What practice can get speed improvement in C++? Bo Persson <bop@gmb.dk> - 2015-08-04 20:09 +0200
            Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-08-04 12:38 -0700
              Re: What practice can get speed improvement in C++? Bo Persson <bop@gmb.dk> - 2015-08-05 17:03 +0200
                Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-08-05 23:32 -0700
            Re: What practice can get speed improvement in C++? Öö Tiib <ootiib@hot.ee> - 2015-08-05 03:55 -0700
          Re: What practice can get speed improvement in C++? Christopher Pisz <nospam@notanaddress.com> - 2015-08-04 14:09 -0500
            Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-08-04 12:18 -0700
              Re: What practice can get speed improvement in C++? Christopher Pisz <nospam@notanaddress.com> - 2015-08-04 14:50 -0500
              Re: What practice can get speed improvement in C++? Öö Tiib <ootiib@hot.ee> - 2015-08-05 04:11 -0700
          Re: What practice can get speed improvement in C++? Juha Nieminen <nospam@thanks.invalid> - 2015-08-05 08:12 +0000
            Re: What practice can get speed improvement in C++? Martin Shobe <martin.shobe@yahoo.com> - 2015-08-05 08:53 -0500
            Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-08-05 22:24 -0700
              Re: What practice can get speed improvement in C++? Ian Collins <ian-news@hotmail.com> - 2015-08-06 17:42 +1200
                Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-08-05 22:53 -0700
                Re: What practice can get speed improvement in C++? Öö Tiib <ootiib@hot.ee> - 2015-08-06 00:20 -0700
                Re: What practice can get speed improvement in C++? Christopher Pisz <nospam@notanaddress.com> - 2015-08-06 10:10 -0500
                Re: What practice can get speed improvement in C++? Bo Persson <bop@gmb.dk> - 2015-08-06 17:29 +0200
                Re: What practice can get speed improvement in C++? woodbrian77@gmail.com - 2015-08-06 09:38 -0700
              Re: What practice can get speed improvement in C++? Juha Nieminen <nospam@thanks.invalid> - 2015-08-10 08:25 +0000
  Re: What practice can get speed improvement in C++? pip010 <pip010@gmail.com> - 2015-08-03 04:22 -0700

csiph-web