Groups > comp.lang.c > #19053

Re: Odd benchmark behavior

From	"BartC" <bc@freeuk.com>
Newsgroups	comp.lang.c
Subject	Re: Odd benchmark behavior
Date	2012-03-26 15:16 +0100
Organization	A noiseless patient Spider
Message-ID	<jkptnr$j8a$1@dont-email.me> (permalink)
References	<9talg3F84gU1@mid.individual.net>

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"Nils M Holm" <news2009@t3x.org> wrote in message 
news:9talg3F84gU1@mid.individual.net...

>                        if (i % p[j] == 0)

> it is in fact abysmally bad. So I was quite surprised to get the
> following run times of the generated programs (median of three
> runs, almost no deviation):
>
> gcc -O2 p.c: 12.39s
> pcc -O p.c: 12.42s
> scc p.c: 12.27s

> I am rather puzzled now. Any ideas?

> idivl %ecx

I suspect the % operation (which needs a divide) dominates the proceedings. 
I put in an extra dummy % op, and it nearly doubled the runtime (3.5 to 6.6 
seconds).

-- 
Bartc

Thread

Odd benchmark behavior Nils M Holm <news2009@t3x.org> - 2012-03-26 07:51 +0000
  Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-03-26 11:26 +0200
    Re: Odd benchmark behavior "BartC" <bc@freeuk.com> - 2012-03-26 10:40 +0100
      Re: Odd benchmark behavior gwowen <gwowen@gmail.com> - 2012-03-26 03:37 -0700
      Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-03-26 14:13 +0200
    Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-03-26 11:55 +0200
      Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-03-27 09:17 +0200
        Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-03-27 09:20 +0200
          Re: Odd benchmark behavior "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2012-03-27 13:39 -0400
          Re: Odd benchmark behavior pete <pfiland@mindspring.com> - 2012-03-27 21:49 -0500
            Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-04-05 12:18 +0200
              Re: Odd benchmark behavior pete <pfiland@mindspring.com> - 2012-04-05 06:48 -0400
                Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-04-05 14:12 +0200
                Re: Odd benchmark behavior pete <pfiland@mindspring.com> - 2012-04-05 09:03 -0400
                Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-04-05 16:18 +0200
                Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-04-07 13:26 +0200
                Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-04-06 09:31 +0200
        Re: Odd benchmark behavior "io_x" <a@b.c.invalid> - 2012-03-27 19:01 +0200
  Re: Odd benchmark behavior "BartC" <bc@freeuk.com> - 2012-03-26 10:36 +0100
    Re: Odd benchmark behavior Nils M Holm <news2009@t3x.org> - 2012-03-26 10:02 +0000
  Re: Odd benchmark behavior Ian Collins <ian-news@hotmail.com> - 2012-03-26 22:58 +1300
  Re: Odd benchmark behavior "BartC" <bc@freeuk.com> - 2012-03-26 15:16 +0100
    Re: Odd benchmark behavior Nils M Holm <news2009@t3x.org> - 2012-03-27 06:20 +0000
      Re: Odd benchmark behavior "BartC" <bc@freeuk.com> - 2012-03-27 10:13 +0100
        Re: Odd benchmark behavior Nils M Holm <news2009@t3x.org> - 2012-03-27 11:59 +0000

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