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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: Request for source code review of simple Ising model |
| Date | 2014-04-18 11:14 -0700 |
| Organization | None to speak of |
| Message-ID | <lntx9q4i95.fsf@nuthaus.mib.org> (permalink) |
| References | (2 earlier) <87wqev6631.fsf@panda.goosenet.in> <87a9bm5qhb.fsf@panda.goosenet.in> <53500B1E.5050404@verizon.net> <lnoazy645u.fsf@nuthaus.mib.org> <5351639A.8040207@verizon.net> |
James Kuyper <jameskuyper@verizon.net> writes:
> On 04/18/2014 11:36 AM, Keith Thompson wrote:
>> James Kuyper <jameskuyper@verizon.net> writes:
> ...
>>> might not be very good, you should be aware of the fact that, in poor
>>> quality implementations, lower-order bits are likely to be significantly
>>> less random than higher-order ones. RAND_MAX is required to be >= 32767,
>>> so 0x4000 is the highest bit that guaranteed to be <RAND_MAX. If you're
>>> only going extract one bit from rand(), I'd recommend extracting that
>>> one: ((rand()%0x4000) == 0x4000 ? 2 : 1).
>>
>> (As discussed downthread, that "%" was meant to be "&".)
>>
>> Is it still the case that the low-order bits are commonly less random
>> than the high-order bits? Question 13.18 of the FAQ
>> <http://www.c-faq.com/> says so, but I suspect it's out of date.
>
> I don't know, which is why I deliberately prefixed my remarks with "in
> poor quality implementations". The average quality of implementation of
> rand() may be improving, but I believe that what I've written is still
> true of poor quality implementations. However, that belief is entirely
> second hand - I can't claim to have performed relevant studies myself.
And the question is, are such poor quality implementations still common
enough that they're worth worrying about? I'm not expecting you to have
a definitive answer to that (nor do I), but if someone else can provide
a concrete example it would be very interesting.
Given that the sample implementation that's been in the standard for the
last 25 years doesn't appear to suffer from this problem[*], there's
really no excuse for any current real-world implementation to be that
bad.
[*] At least it doesn't return 0, 1, 0, 1, ... for the low-order bit.
It *might* still be the case that the low-order bits are lower quality
than the high-order bits. I lack the expertise to analyze it.
--
Keith Thompson (The_Other_Keith) kst-u@mib.org <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something. This is something. Therefore, we must do this."
-- Antony Jay and Jonathan Lynn, "Yes Minister"
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Request for source code review of simple Ising model Udyant Wig <udyant@panda.goosenet.in> - 2014-04-10 23:38 +0530
Re: Request for source code review of simple Ising model Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-10 13:30 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-12 00:34 +0530
Re: Request for source code review of simple Ising model Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-11 12:25 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-16 01:12 +0530
Re: Request for source code review of simple Ising model Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-04-16 01:33 +0100
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-16 17:57 +0530
Re: Request for source code review of simple Ising model Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-16 06:00 -0700
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-16 10:58 -0400
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-16 09:07 -0700
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-16 12:22 -0400
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-16 10:38 -0700
Re: Request for source code review of simple Ising model Kaz Kylheku <kaz@kylheku.com> - 2014-04-16 19:37 +0000
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-17 12:00 +0530
Re: Request for source code review of simple Ising model glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-17 09:32 +0000
Re: Request for source code review of simple Ising model "BartC" <bc@freeuk.com> - 2014-04-17 12:24 +0100
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-17 08:16 -0700
Re: Request for source code review of simple Ising model Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-17 04:41 -0700
Re: Request for source code review of simple Ising model Les Cargill <lcargill99@comcast.com> - 2014-04-17 07:49 -0500
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-17 08:00 -0700
Re: Request for source code review of simple Ising model Kaz Kylheku <kaz@kylheku.com> - 2014-04-17 15:06 +0000
Re: Request for source code review of simple Ising model Tim Rentsch <txr@alumni.caltech.edu> - 2014-04-18 21:04 -0700
Re: Request for source code review of simple Ising model glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-17 18:38 +0000
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-17 15:26 -0400
Re: Request for source code review of simple Ising model "BartC" <bc@freeuk.com> - 2014-04-17 21:00 +0100
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-17 16:34 -0400
Re: Request for source code review of simple Ising model glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-18 04:31 +0000
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-17 14:05 -0700
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-17 17:06 -0700
Re: Request for source code review of simple Ising model glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-18 04:54 +0000
Re: Request for source code review of simple Ising model Tim Rentsch <txr@alumni.caltech.edu> - 2014-04-18 11:51 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-17 11:42 +0530
Re: Request for source code review of simple Ising model Ben Bacarisse <ben.usenet@bsb.me.uk> - 2014-04-16 16:54 +0100
Re: Request for source code review of simple Ising model Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-16 15:22 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-17 13:03 +0530
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-17 08:44 -0700
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-17 12:12 -0400
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-18 12:38 +0530
Re: Request for source code review of simple Ising model Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-18 03:11 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-18 12:32 +0530
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-18 10:05 -0400
Re: Request for source code review of simple Ising model Ike Naar <ike@iceland.freeshell.org> - 2014-04-16 07:10 +0000
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-17 13:10 -0400
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-18 18:24 +0530
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-18 09:52 -0400
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-18 20:04 +0530
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-18 11:00 -0400
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-20 01:49 +0530
Re: Request for source code review of simple Ising model glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2014-04-19 21:20 +0000
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-20 11:11 +0530
Re: Request for source code review of simple Ising model Richard Damon <Richard@Damon-Family.org> - 2014-04-20 09:06 -0400
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-20 10:50 -0400
Re: Request for source code review of simple Ising model Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-21 09:14 -0700
Re: Request for source code review of simple Ising model Ike Naar <ike@iceland.freeshell.org> - 2014-04-19 05:43 +0000
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-18 19:47 +0530
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-21 01:21 +0530
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-20 14:24 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-21 10:40 +0530
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-21 12:29 +0530
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-18 08:36 -0700
Re: Request for source code review of simple Ising model James Kuyper <jameskuyper@verizon.net> - 2014-04-18 13:40 -0400
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-18 11:14 -0700
Re: Request for source code review of simple Ising model Malcolm McLean <malcolm.mclean5@btinternet.com> - 2014-04-18 13:55 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-19 01:25 +0530
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-19 01:44 +0530
Re: Request for source code review of simple Ising model Kaz Kylheku <kaz@kylheku.com> - 2014-04-18 20:24 +0000
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-18 13:36 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-19 20:18 +0530
Re: Request for source code review of simple Ising model Richard <rgrdev_@gmail.com> - 2014-04-19 14:55 +0100
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-20 02:10 +0530
Re: Request for source code review of simple Ising model Ike Naar <ike@iceland.freeshell.org> - 2014-04-19 05:40 +0000
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-19 14:39 -0700
Re: Request for source code review of simple Ising model Ian Collins <ian-news@hotmail.com> - 2014-04-20 10:44 +1200
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-19 17:11 -0700
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-20 11:24 +0530
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-19 17:19 -0700
Re: Request for source code review of simple Ising model Ike Naar <ike@iceland.freeshell.org> - 2014-04-20 10:10 +0000
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-20 14:21 -0700
Re: Request for source code review of simple Ising model Ike Naar <ike@iceland.freeshell.org> - 2014-04-20 22:18 +0000
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-20 19:27 -0700
Re: Request for source code review of simple Ising model Ike Naar <ike@iceland.freeshell.org> - 2014-04-21 12:38 +0000
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-21 18:12 +0530
Re: Request for source code review of simple Ising model Ike Naar <ike@iceland.freeshell.org> - 2014-04-21 13:13 +0000
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-21 19:46 +0530
Re: Request for source code review of simple Ising model Keith Thompson <kst-u@mib.org> - 2014-04-21 09:06 -0700
Re: Request for source code review of simple Ising model jacob navia <jacob@spamsink.net> - 2014-04-21 00:26 +0200
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-18 01:15 +0530
Re: Request for source code review of simple Ising model Udyant Wig <udyantw@gmail.com> - 2014-04-20 11:46 +0530
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