Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.c++ > #8884
| From | "Paul" <pchristor@yahoo.co.uk> |
|---|---|
| Newsgroups | comp.lang.c++ |
| Subject | Re: maximum cases in a switch ? |
| Date | 2011-08-16 03:10 +0100 |
| Organization | Netfront http://www.netfront.net/ |
| Message-ID | <j2cjib$1is5$1@adenine.netfront.net> (permalink) |
| References | (15 earlier) <j2bcls$2gk$1@adenine.netfront.net> <voKdneBY59LDpNTTnZ2dnUVZ8t2dnZ2d@giganews.com> <j2brqu$o31$1@adenine.netfront.net> <9tCdnZfs3uFkF9TTnZ2dnUVZ8qmdnZ2d@giganews.com> <dLWdnag7luznENTTnZ2dnUVZ8jidnZ2d@giganews.com> |
"Leigh Johnston" <leigh@i42.co.uk> wrote in message
news:dLWdnag7luznENTTnZ2dnUVZ8jidnZ2d@giganews.com...
> On 15/08/2011 22:09, Leigh Johnston wrote:
>> On 15/08/2011 20:24, Paul wrote:
>>>
>>> "Leigh Johnston" <leigh@i42.co.uk> wrote in message
>>> news:voKdneBY59LDpNTTnZ2dnUVZ8t2dnZ2d@giganews.com...
>>>> On 15/08/2011 16:05, Paul 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".
>>>>>>>>
>>>>>>>> His opinion is that it is *just* 6 clock cycles not 6x525 clock
>>>>>>>> cycles; your lack of comprehension and naivity is stunning. Again:
>>>>>>>> learn about jump tables instead of wasting time displaying a lack
>>>>>>>> of
>>>>>>>> knowledge here.
>>>>>>>>
>>>>>>> You can't have a switch statement with 525 cases executed in 6 clock
>>>>>>> cycles you fucking moronic idiot.
>>>>>>
>>>>>> Your insults do nothing to mend your reputation or make your
>>>>>> incorrect
>>>>>> assertions correct.
>>>>>>
>>>>> Well stop being a moron. The only thing incorrect here is your
>>>>> incorrect
>>>>> assumption that I was talking about jump tables.
>>>>>
>>>>> A compiler is free to implement a switch statement anyway it likes.
>>>>> All
>>>>> I was saying that with the worst case scenario of a 525 switch case
>>>>> statement is may be something like 1500 clock cycles which is not
>>>>> really
>>>>> alot of CPU time anyway, even though 525 cases seems like a lot.
>>>>> It may be more it may be less, I don't know how the compiler will
>>>>> implement it and neither do you. You do not the full details of the
>>>>> code
>>>>> , does it have a default statement etc, which compiler is it , blah
>>>>> blah
>>>>> blah.
>>>>>
>>>>> So please stop making inciorrect assumptions that I was talking about
>>>>> jump tables , and trying to start an argument based on the false
>>>>> assumption that you know what a jump table is and I don't.
>>>>> I don't know why you havent learned your lesson from the past , I
>>>>> guess
>>>>> you are just going to keep on arguing and creating arguments until you
>>>>> actually win one. And before you start bringing up history and
>>>>> trying to
>>>>> falsify who had he victorious outcome please remember this:
>>>>>
>>>>> int x = new int[24];
>>>>> x is a pointer to an array of integers. :)
>>>>
>>>> You said: "You can't have a switch statement with 525 cases executed
>>>> in 6 clock cycles you fucking moronic idiot." (just scroll up). This
>>>> assertion is false and I explained why whilst also introducing you to
>>>> the concept of jump tables (a thankyou would be nice).
>>>
>>> The assertion is true.
>>> The switch statement does not have ordered cases therefore you could
>>> only implement this with a hash table but then you are basically
>>> rewriting the software completely and you no longer have a switch
>>> statement.
>>
>> From an earlier reply of mine that you seemed to have ignored:
>>
>> "For another clue think about the difference between a switch with
>> contiguous case values and non-contiguous case values. *Most* switches
>> have contiguous case values. If you have a switch with 525
>> non-contiguous case values then you may well need 6x525 clock cycles if
>> again the solution was naive solution (a non-naive solution would be to
>> use binary search on a jump table)."
>>
>> So your assertion remains false and you continue to fail.
>>
>> HTH.
>>
>
> Funnily enough I have implemented switch statements in my own programming
> language using the binary search method which actually allowed me to
> supported mixed case types (other than basic integers):
omg , your language?
What do you call this language you are creating/have created?
>
> for (int i = 1; i < 4; ++i)
> {
> var v;
> switch(i)
> {
> case 1:
> v = 123;
> break;
> case 2:
> v = "abc";
> break;
> case 3:
> v = 1.01;
> break;
> }
> switch(v)
> {
> case 123L:
> print_line(v + " is an integer");
> break;
> case "abc":
> print_line(v + " is a string");
> break;
> default:
> print_line(v + " is a neither an integer nor a string");
> break;
> }
> switch(v)
> {
> case 123:
> case "abc":
> print_line(v + " is an integer or a string");
> break;
> default:
> print_line(v + " is a neither an integer nor a string");
> break;
> }
> }
>
> Although off-topic I thought it quite interesting and cromulent to the
> discussion.
>
Is the above code your language or C++?
--- Posted via news://freenews.netfront.net/ - Complaints to news@netfront.net ---
Back to comp.lang.c++ | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll 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
csiph-web