Re: maximum cases in a switch ?

From	"Paul" <pchristor@yahoo.co.uk>
Newsgroups	comp.lang.c++
Subject	Re: maximum cases in a switch ?
Date	2011-08-15 12:18 +0100
Organization	Netfront http://www.netfront.net/
Message-ID	<j2avah$2htu$1@adenine.netfront.net> (permalink)
References	(6 earlier) <3uydnS2bVrh7LtjTnZ2dnUVZ7vGjnZ2d@giganews.com> <j25vnh$307c$1@adenine.netfront.net> <4e48109f$0$2874$7b1e8fa0@news.nbl.fi> <j29o5d$vlt$1@adenine.netfront.net> <8740e3fe-8a70-4d59-bead-66ac3485b009@k3g2000vbz.googlegroups.com>

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"Nick Keighley" <nick_keighley_nospam@hotmail.com> wrote in message 
news:8740e3fe-8a70-4d59-bead-66ac3485b009@k3g2000vbz.googlegroups.com...
On Aug 15, 1:09 am, "Paul" <pchris...@yahoo.co.uk> wrote:
> "Juha Nieminen" <nos...@thanks.invalid> wrote in message
>
> news:4e48109f$0$2874$7b1e8fa0@news.nbl.fi...
>
> > Paul <pchris...@yahoo.co.uk> wrote:
> >>>> 525 switch cases seem alot but how long does this take to compute,
> >>>> assuming the very last case is the one that is true? Probably not 
> >>>> very
> >>>> long, maybe 3 instructions per conditional test, so it might be 
> >>>> around
> >>>> 1500 clock cycles or something.
>
> >>> Only if the compiler was as naive as you (for a clue you should learn
> >>> about jump tables).
>
> >> From behind which rock have you crawled?
>
> > Please explain to us how using a jump table to implement a switch block
> > of 525 cases could possibly take 1500 clock cycles.
>
> I already have explained it, obviosly this is a very rough estimate

--ITYM "wrong estimate"

There is no "right" estimate, a quadcore cpu  with precaching and all the 
fancy tech they have nowadays will probably do it alot faster than an 
ancient AMD cpu.

So you are "wrong" to say my estimate was "wrong".

> as not
> all CPU's are the same. Can you explain how many clock cycles you think 
> it'd
> take?

--the number taken is independent of the number of entries in the table

 --   goto table[i];

--we're talking half a dozen instructions and a couple of memory
--accesses

Start Process:
Load reg1 with comparee (Only done once at start)

Load reg2 with case option
Load reg3 with jump address
Jump if reg1and reg2 are equal .

repeat above until the condition is met.

Why do you need to repeat 6 instructions ?
And what are you talking about memeory access? L1 cache? or pipeline cache 
or prefetched queues?
Modern CPUs have everything all prefetched into caches and its a bit more 
complicated than you seem to understand.
You can try to pretend you know more than me about it and I don't really 
care if you do or don't but when you challenge something I said as wrong and 
present "your opinion" as right, I'd suggest you get your facts right first 
and provide some kind of evidence which supports your "claim".

Even if your opinion that it was 6x525 clock cycles , for any given CPU, was 
100% exact then  that would make my estimate close enough to be accurate, 
because we are talking about cpu speeds in gigahertz now.
Please don't claim my estimates are "wrong" without providing some kind of 
reason other that "because you say so".

--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---

Thread

maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-09 11:03 -0500
  Re: maximum cases in a switch ? LR <lruss@superlink.net> - 2011-08-09 12:27 -0400
    Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-09 12:23 -0500
      Re: maximum cases in a switch ? Joe Greer <jgreer@doubletake.com> - 2011-08-10 12:45 +0000
        Re: maximum cases in a switch ? Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-10 09:09 -0400
          Re: maximum cases in a switch ? Joe Greer <jgreer@doubletake.com> - 2011-08-11 12:49 +0000
            Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-11 10:48 -0500
              Re: maximum cases in a switch ? Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-08-11 18:26 +0200
                Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-11 11:45 -0500
                Re: maximum cases in a switch ? Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-08-11 20:06 +0200
                Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-11 14:47 -0500
                Re: maximum cases in a switch ? Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-08-11 22:32 +0200
                Re: maximum cases in a switch ? gwowen <gwowen@gmail.com> - 2011-08-12 06:00 -0700
                Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-12 10:49 -0500
              Re: maximum cases in a switch ? Joe Greer <jgreer@doubletake.com> - 2011-08-12 13:46 +0000
                Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-12 10:58 -0500
                Re: maximum cases in a switch ? Joe Greer <jgreer@doubletake.com> - 2011-08-12 20:22 +0000
                Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-12 15:57 -0500
                Re: maximum cases in a switch ? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-08-13 20:58 +0200
                Re: maximum cases in a switch ? Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-13 18:16 -0400
                Re: maximum cases in a switch ? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-08-16 07:55 +0200
                Re: maximum cases in a switch ? Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-16 09:04 -0400
                Re: maximum cases in a switch ? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-08-17 00:11 +0200
                Re: maximum cases in a switch ? Ian Collins <ian-news@hotmail.com> - 2011-08-17 10:24 +1200
                Re: maximum cases in a switch ? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-08-17 01:33 +0200
                Re: maximum cases in a switch ? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-08-17 00:18 +0200
                Re: maximum cases in a switch ? Ian Collins <ian-news@hotmail.com> - 2011-08-17 10:29 +1200
                Re: maximum cases in a switch ? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-08-17 01:37 +0200
                Re: maximum cases in a switch ? Ian Collins <ian-news@hotmail.com> - 2011-08-17 12:02 +1200
  Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-09 16:38 +0000
  Re: maximum cases in a switch ? Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-09 15:42 -0400
    Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-09 15:39 -0500
      Re: maximum cases in a switch ? Leo Equinox Gaspard <ekinox1995@gmail.com> - 2011-08-09 23:39 +0200
        Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-09 17:18 -0500
      Re: maximum cases in a switch ? Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-09 20:06 -0400
        Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-10 06:54 +0000
          Re: maximum cases in a switch ? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-10 12:20 +0000
            Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-10 11:34 -0500
              Re: maximum cases in a switch ? Paul Brettschneider <paul.brettschneider@yahoo.fr> - 2011-08-10 20:34 +0200
                Re: maximum cases in a switch ? Paul Brettschneider <paul.brettschneider@yahoo.fr> - 2011-08-10 21:06 +0200
              Re: maximum cases in a switch ? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-08-11 21:00 +0000
      Re: maximum cases in a switch ? Marcel Müller <news.5.maazl@spamgourmet.com> - 2011-08-10 11:10 +0200
        Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-10 10:40 +0000
          Re: maximum cases in a switch ? Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-10 09:02 -0400
            Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-11 08:05 +0000
          Re: maximum cases in a switch ? Marcel Müller <news.5.maazl@spamgourmet.com> - 2011-08-10 21:17 +0200
        Re: maximum cases in a switch ? Lynn McGuire <lmc@winsim.com> - 2011-08-10 11:12 -0500
          Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-11 11:07 +0100
            Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-13 00:14 +0100
              Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-13 14:54 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-13 15:26 +0100
                Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-14 18:14 +0000
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-15 01:09 +0100
                Re: maximum cases in a switch ? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-08-15 02:15 -0700
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-15 12:18 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-15 13:22 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-15 13:38 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-15 14:06 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-15 16:05 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-15 16:20 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-15 20:24 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-15 22:09 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-15 22:19 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-16 03:10 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-16 13:08 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-16 14:01 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-16 14:10 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-16 03:07 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-16 13:05 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-16 13:57 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-16 14:07 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-16 19:29 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-16 19:35 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 00:01 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-17 00:11 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 01:23 +0100
                Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-15 13:32 +0000
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-15 15:20 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-15 15:33 +0100
                Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-16 07:34 +0000
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-16 13:49 +0100
                Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-16 15:02 +0000
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-16 16:07 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-16 19:50 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-16 19:57 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 00:12 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-16 19:34 +0100
                Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-17 12:55 +0000
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 14:32 +0100
                Re: maximum cases in a switch ? Juha Nieminen <nospam@thanks.invalid> - 2011-08-17 20:11 +0000
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-18 11:00 +0100
                Re: maximum cases in a switch ? Joshua Maurice <joshuamaurice@gmail.com> - 2011-08-15 15:35 -0700
                Re: maximum cases in a switch ? Gareth Owen <gwowen@gmail.com> - 2011-08-17 06:34 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 12:23 +0100
                Re: maximum cases in a switch ? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-08-17 02:01 -0700
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 12:29 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-17 14:13 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 14:18 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-17 14:43 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 15:23 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-17 15:31 +0100
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 15:48 +0100
                Re: maximum cases in a switch ? Leigh Johnston <leigh@i42.co.uk> - 2011-08-17 15:53 +0100
                Re: maximum cases in a switch ? SG <s.gesemann@gmail.com> - 2011-08-17 07:54 -0700
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 20:40 +0100
                Re: maximum cases in a switch ? Larry Evans <cppljevans@suddenlink.net> - 2011-08-17 10:54 -0500
                Re: maximum cases in a switch ? Robert Wessel <robertwessel2@yahoo.com> - 2011-08-17 12:44 -0500
                jump table vs. vector of function pointers(was Re: maximum cases in a switch ? Larry Evans <cppljevans@suddenlink.net> - 2011-08-17 15:18 -0500
                Re: jump table vs. vector of function pointers(was Re: maximum cases in a switch ? Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2011-08-17 22:48 +0200
                Re: jump table vs. vector of function pointers(was Re: maximum cases in a switch ? Larry Evans <cppljevans@suddenlink.net> - 2011-08-17 16:49 -0500
                Re: maximum cases in a switch ? Thomas David Rivers <rivers@dignus.com> - 2011-08-17 13:50 -0400
                Re: maximum cases in a switch ? "Paul" <pchristor@yahoo.co.uk> - 2011-08-17 22:04 +0100
                Re: maximum cases in a switch ? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-08-22 03:23 -0700
    Re: maximum cases in a switch ? Nick Keighley <nick_keighley_nospam@hotmail.com> - 2011-08-12 05:51 -0700
      Re: maximum cases in a switch ? Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-13 08:45 -0400
    Re: maximum cases in a switch ? James Kanze <james.kanze@gmail.com> - 2011-08-21 16:55 -0700
      Re: maximum cases in a switch ? Robert Wessel <robertwessel2@yahoo.com> - 2011-08-21 23:22 -0500
        Re: maximum cases in a switch ? Victor Bazarov <v.bazarov@comcast.invalid> - 2011-08-22 08:14 -0400
        Re: maximum cases in a switch ? James Kanze <james.kanze@gmail.com> - 2011-08-22 10:56 -0700

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