Re: harder case for optimization

From	Melzzzzz <mel@zzzzz.com>
Newsgroups	comp.lang.c
Subject	Re: harder case for optimization
Date	2014-11-28 21:03 +0100
Organization	albasani.net
Message-ID	<20141128210320.53d6e8c2@maxa-pc> (permalink)
References	(7 earlier) <22%dw.11896$He3.4668@fx15.am4> <m5a455$tf3$1@dont-email.me> <e3485f9b-51d4-4c36-b3cc-4e6f10dd395a@googlegroups.com> <m5ai1a$mqi$1@dont-email.me> <20141128114639.902@kylheku.com>

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On Fri, 28 Nov 2014 19:51:39 +0000 (UTC)
Kaz Kylheku <kaz@kylheku.com> wrote:

> On 2014-11-28, David Brown <david.brown@hesbynett.no> wrote:
> > I expect that any programmer who is capable of "hand-optimising" a
> > division into a multiplication knows that dividing by 16 is easier
> > than dividing by 13.
> 
> A programmer who *doesn't* know that / 13 can be turned into a
> multiplication thinks that dividing by 13 is an utter disaster
> compared to 16. :)

Heh, compilers do that for us ;)
I just look into generated constant and that's it ...
What surprised me is that Java doesn't do division
by multiplication even when it performs pretty advanced
optimization's. 
gcc does integer division by multiplication, but it does not
do that for floats. So eg if one writes x/13.5 it will
generate division instruction , which is much slower than x*(1.0/13.5).

Thread

harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 00:42 -0800
  Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-27 11:34 +0000
    Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-27 13:29 +0100
    Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-27 05:58 -0800
      Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-27 06:36 -0800
    Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 12:26 -0800
  Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-27 22:07 +0000
    Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 14:49 -0800
      Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 00:05 +0000
    Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 00:46 +0100
      Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 00:55 +0000
        Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 07:20 +0100
          Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 00:41 -0800
            Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 01:54 -0800
              Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 02:19 -0800
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 04:05 -0800
                Closed captioning (Was: harder case for something or other) gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-28 12:15 +0000
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 06:11 -0800
              Re: harder case for optimization gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-28 12:18 +0000
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 04:42 -0800
                Re: harder case for optimization gazelle@shell.xmission.com (Kenny McCormack) - 2014-11-28 16:37 +0000
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 08:48 -0800
                Re: harder case for optimization Kaz Kylheku <kaz@kylheku.com> - 2014-11-28 16:51 +0000
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 10:38 -0800
            Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 11:34 +0100
          Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 11:21 +0000
            Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 04:23 -0800
            Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 13:58 +0100
              Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 13:46 +0000
                Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 16:25 +0100
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 08:18 -0800
                Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 20:17 +0100
                Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 08:54 -0800
                Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 20:22 +0100
                Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-28 11:29 -0800
                Re: harder case for optimization Kaz Kylheku <kaz@kylheku.com> - 2014-11-28 19:51 +0000
                Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 20:58 +0100
                Re: harder case for optimization Melzzzzz <mel@zzzzz.com> - 2014-11-28 21:03 +0100
                Re: harder case for optimization Kaz Kylheku <kaz@kylheku.com> - 2014-11-28 20:11 +0000
                Re: harder case for optimization Melzzzzz <mel@zzzzz.com> - 2014-11-28 21:31 +0100
                Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 20:06 +0000
                Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 17:14 +0000
                Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 20:54 +0100
                Re: harder case for optimization "BartC" <bc@freeuk.com> - 2014-11-28 20:16 +0000
                Re: harder case for optimization David Brown <david.brown@hesbynett.no> - 2014-11-28 21:56 +0100
        Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 23:37 -0800
          Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-27 23:54 -0800
          Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-28 11:01 +0000
            Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-28 23:52 -0800
              Re: harder case for optimization Morris Dovey <mrdovey@iedu.com> - 2014-11-29 02:03 -0600
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 00:38 -0800
  Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 03:12 -0800
    Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-29 12:09 +0000
      Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 04:18 -0800
      Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 05:22 -0800
        Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-29 16:58 +0000
          Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 09:35 -0800
          Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-29 10:55 -0800
            Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-29 21:00 +0000
              Re: harder case for optimization Ian Collins <ian-news@hotmail.com> - 2014-11-30 11:25 +1300
                Re: harder case for optimization BartC <bc@freeuk.com> - 2014-11-29 22:56 +0000
                Re: harder case for optimization Ian Collins <ian-news@hotmail.com> - 2014-11-30 12:00 +1300
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 16:01 -0800
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 16:21 -0800
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 16:52 -0800
                Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-11-29 17:14 -0800
            Re: harder case for optimization glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-11-30 00:20 +0000
              Re: harder case for optimization Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-11-29 16:43 -0800
        Re: harder case for optimization Kaz Kylheku <kaz@kylheku.com> - 2014-11-29 17:29 +0000
  Re: harder case for optimization fir <profesor.fir@gmail.com> - 2014-12-05 02:12 -0800

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