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| From | Shao Miller <sha0.miller@gmail.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Short-circuiting in C |
| Date | 2011-05-27 09:28 -0400 |
| Organization | A noiseless patient Spider |
| Message-ID | <iro8or$sb2$1@dont-email.me> (permalink) |
| References | (4 earlier) <threads-20110526210028@ram.dialup.fu-berlin.de> <irm8kv$hgm$1@speranza.aioe.org> <branch-20110526213137@ram.dialup.fu-berlin.de> <irmv5h$4on$1@speranza.aioe.org> <lnboyoveao.fsf@nuthaus.mib.org> |
On 5/27/2011 02:38, Keith Thompson wrote:
> Billy Mays<noway@nohow.com> writes:
>> On 5/26/2011 3:32 PM, Stefan Ram wrote:
>>> Billy Mays<noway@nohow.com> writes:
>>>> For example,
>>>> if(a&& b&& c) {
>>>> /* Do stuff */
>>>> }
>>>> Neither thread will execute the body of the if statement, but Thread 2
>>>> would branch away while Thread 1 would still be evaluating b and c.
>>>
>>> Yes. The above is
>>>
>>> if(a)if(b)if(c)
>>> {}
>>>
>>> (as long as not followed by an »else«).
>>>
>>
>> I believe this will work, thanks!
>
> You do? The point was to avoid differing branches depending on
> differing values of a, b, and c. In the if() form, the branches are,
> in some sense, even more explicit than in the&& form.
>
Agreed. I don't understand exactly what the original poster wants to
achieve, but my impression is that they want "lock-steppedness." :)
> The problem is that the C language defines *behavior*, and you're trying
> to control the manner in which that behavior is created, i.e., the
> sequence of machine-level operations. There's no 100% reliable way to
> do that.
>
Agreed. But one can make some educated guesses about the timing of
operations. In the table-using code I posted else-thread, if the 'func'
function is called with different arguments simultaneously, those
invocations should return the result simultaneously, barring external
interruptions. Of course, such a table strategy becomes unwieldy as
more parameters are required; heh.
> Of course you're going to have *some* inconsistent branching; depending
> on the values of a, b, and c, each thread will or will not execute the
> body of the if statement. So you're trying to minimize the possible
> differences in branching.
>
> I think your best bet is probably to try a few possible solutions and
> examine the generated assembly or machine language for each one.
Agreed. The 'gcc -save-temps' is handy for examining resulting '.s'
files. This shows that the table-using code doesn't have any branches
(excluding the function calls). Of course, 'gcc' mightn't be applicable
to the original poster's OpenCL needs.
Loops change timing, of course.
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Short-circuiting in C Billy Mays <noway@nohow.com> - 2011-05-26 13:58 -0400
Re: Short-circuiting in C Ben Pfaff <blp@cs.stanford.edu> - 2011-05-26 11:09 -0700
Re: Short-circuiting in C Thomas Richter <thor@math.tu-berlin.de> - 2011-05-26 20:22 +0200
Re: Short-circuiting in C Ben Pfaff <blp@cs.stanford.edu> - 2011-05-26 11:35 -0700
Re: Short-circuiting in C falk@rahul.net (Edward A. Falk) - 2011-05-31 18:45 +0000
Re: Short-circuiting in C Nizumzen <chicken@mcnuggets.com> - 2011-05-31 20:31 +0100
Re: Short-circuiting in C Billy Mays <noway@nohow.com> - 2011-05-26 14:51 -0400
Re: Short-circuiting in C Billy Mays <noway@nohow.com> - 2011-05-26 15:10 -0400
Re: Short-circuiting in C Billy Mays <noway@nohow.com> - 2011-05-26 21:35 -0400
Re: Short-circuiting in C Keith Thompson <kst-u@mib.org> - 2011-05-26 23:38 -0700
Re: Short-circuiting in C Shao Miller <sha0.miller@gmail.com> - 2011-05-27 09:28 -0400
Re: Short-circuiting in C falk@rahul.net (Edward A. Falk) - 2011-05-31 19:01 +0000
Re: Short-circuiting in C falk@rahul.net (Edward A. Falk) - 2011-05-31 19:02 +0000
Re: Short-circuiting in C Keith Thompson <kst-u@mib.org> - 2011-05-26 12:55 -0700
Re: Short-circuiting in C Billy Mays <noway@nohow.com> - 2011-05-26 16:17 -0400
Re: Short-circuiting in C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-26 21:28 -0400
Re: Short-circuiting in C Seebs <usenet-nospam@seebs.net> - 2011-05-27 05:06 +0000
Re: Short-circuiting in C Noob <root@127.0.0.1> - 2011-05-27 17:48 +0200
Re: Short-circuiting in C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-27 21:31 -0400
Re: Short-circuiting in C blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-05-28 03:28 +0000
Re: Short-circuiting in C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-27 23:43 -0400
Re: Short-circuiting in C blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-05-28 19:31 +0000
Re: Short-circuiting in C Michael Press <rubrum@pacbell.net> - 2011-05-30 00:28 -0700
Re: Short-circuiting in C BGB <cr88192@hotmail.com> - 2011-05-30 23:08 -0700
Re: Short-circuiting in C Michael Press <rubrum@pacbell.net> - 2011-05-31 18:30 -0700
Re: Short-circuiting in C BGB <cr88192@hotmail.com> - 2011-06-02 09:08 -0700
Re: Short-circuiting in C Nobody <nobody@nowhere.com> - 2011-05-28 14:08 +0100
Re: Short-circuiting in C BGB <cr88192@hotmail.com> - 2011-05-28 12:52 -0700
Re: Short-circuiting in C falk@rahul.net (Edward A. Falk) - 2011-05-31 19:22 +0000
Re: Short-circuiting in C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-31 21:07 -0400
Re: Short-circuiting in C Dr Nick <3-nospam@temporary-address.org.uk> - 2011-06-11 17:07 +0100
Re: Short-circuiting in C Shao Miller <sha0.miller@gmail.com> - 2011-06-11 12:57 -0500
Re: Short-circuiting in C "Morris Keesan" <mkeesan@post.harvard.edu> - 2011-05-26 14:36 -0400
Re: Short-circuiting in C "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2011-05-26 14:39 -0400
Re: Short-circuiting in C Keith Thompson <kst-u@mib.org> - 2011-05-26 13:28 -0700
Re: Short-circuiting in C Urist Sethkab <uristqwerty@gmail.com> - 2011-05-26 15:34 -0700
Re: Short-circuiting in C "Scott Fluhrer" <sfluhrer@ix.netcom.com> - 2011-05-27 10:08 -0400
Re: Short-circuiting in C Keith Thompson <kst-u@mib.org> - 2011-05-27 07:56 -0700
Re: Short-circuiting in C Geoff <geoff@invalid.invalid> - 2011-05-27 20:14 -0700
Re: Short-circuiting in C Keith Thompson <kst-u@mib.org> - 2011-05-27 20:26 -0700
Re: Short-circuiting in C Geoff <geoff@invalid.invalid> - 2011-05-27 20:44 -0700
Re: Short-circuiting in C Nobody <nobody@nowhere.com> - 2011-05-27 00:06 +0100
Re: Short-circuiting in C Billy Mays <noway@nohow.com> - 2011-05-26 21:34 -0400
Re: Short-circuiting in C Nobody <nobody@nowhere.com> - 2011-05-27 07:41 +0100
Re: Short-circuiting in C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-05-26 21:21 -0400
Re: Short-circuiting in C Shao Miller <sha0.miller@gmail.com> - 2011-05-26 20:41 -0500
Re: Short-circuiting in C Shao Miller <sha0.miller@gmail.com> - 2011-05-26 21:03 -0500
Re: Short-circuiting in C Shao Miller <sha0.miller@gmail.com> - 2011-05-26 21:37 -0500
Re: Short-circuiting in C ImpalerCore <jadill33@gmail.com> - 2011-05-27 09:01 -0700
Re: Short-circuiting in C Willem <willem@toad.stack.nl> - 2011-05-27 16:08 +0000
Re: Short-circuiting in C ImpalerCore <jadill33@gmail.com> - 2011-05-27 09:46 -0700
Re: Short-circuiting in C BGB <cr88192@hotmail.com> - 2011-05-28 13:27 -0700
Re: Short-circuiting in C James Kuyper <jameskuyper@verizon.net> - 2011-05-28 09:44 -0400
Re: Short-circuiting in C Keith Thompson <kst-u@mib.org> - 2011-05-28 12:15 -0700
Re: Short-circuiting in C James Kuyper <jameskuyper@verizon.net> - 2011-05-28 17:07 -0400
Re: Short-circuiting in C "Herbert Rosenau" <os2guy@pc-rosenau.de> - 2011-05-29 07:25 +0000
Re: Short-circuiting in C falk@rahul.net (Edward A. Falk) - 2011-05-31 18:40 +0000
Re: Short-circuiting in C BGB <cr88192@hotmail.com> - 2011-06-02 09:48 -0700
Re: Short-circuiting in C Eric Sosman <esosman@ieee-dot-org.invalid> - 2011-06-02 21:05 -0400
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