Re: Compare two methods of random permutations

From	pacman@kosh.dhis.org (Alan Curry)
Newsgroups	comp.programming
Subject	Re: Compare two methods of random permutations
Date	2013-05-16 06:57 +0000
Organization	Aioe.org NNTP Server
Message-ID	<kn201c$5vp$1@speranza.aioe.org> (permalink)
References	<kmegeh$921$1@news.albasani.net> <csSdndTRgvcICg7MnZ2dnUVZ_vednZ2d@earthlink.com> <5f7c6014-dde2-4604-9f30-c544f3a336bb@k8g2000pbf.googlegroups.com> <O-CdnaNSZ9AA9wnMnZ2dnUVZ8gudnZ2d@bt.com>

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In article <O-CdnaNSZ9AA9wnMnZ2dnUVZ8gudnZ2d@bt.com>,
Chris Uppal <chris.uppal@metagnostic.REMOVE-THIS.org> wrote:
>James Dow Allen wrote:
>
>> Duh. Yeah.  Note that the code snippet I posted assures, via
>>          do a = rand();
>>         while (a >= 1916006400);
>> that the requirements are met throughout.
>
>Missed that aspect of it myself.  Shows the value of comments in code...
>
>But, why 1916006400 ?  I may be missing something but it seems to me that 
>239500800 (12! / 2) would work just as well and not have a confusing/misleading 
>factor of 8 mismatch with the code.

Whenever rand() returns something bigger than 1916006400 you have to call it
again. And keep calling it until it gives you something good. If you lower
the limit, you'll spend more time in the loop waiting for a usable random
number.

1916006400 is the largest multiple of 239500800 that fits in a signed 32-bit
integer, so it minimizes the number of rand() results that have to be thrown
away. If your rand() doesn't return a signed 32-bit integer you should adjust
the constant accordingly.

-- 
Alan Curry

Thread

Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-08 23:35 +0200
  Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-11 21:31 -0700
    Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-13 08:07 +0200
      Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-13 02:34 -0700
  Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-13 08:01 +0200
  Re: Compare two methods of random permutations bob <bob@coolfone.comze.com> - 2013-05-13 08:26 -0700
    Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-13 11:42 -0700
      Re: Compare two methods of random permutations bob <bob@coolfone.comze.com> - 2013-05-16 13:46 -0700
    Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-13 21:09 +0200
      Re: Compare two methods of random permutations bob <bob@coolfone.comze.com> - 2013-05-13 12:57 -0700
        Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-13 22:59 +0200
          Re: Compare two methods of random permutations bob <bob@coolfone.comze.com> - 2013-05-13 15:28 -0700
            Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-14 10:54 +0200
              Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-14 05:32 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-14 22:46 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-14 14:19 -0700
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-14 15:06 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-15 10:16 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-15 03:54 -0700
                Re: Compare two methods of random permutations Patricia Shanahan <pats@acm.org> - 2013-05-15 07:11 -0700
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-15 11:04 -0700
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-15 11:06 -0700
                Re: Compare two methods of random permutations Patricia Shanahan <pats@acm.org> - 2013-05-15 12:55 -0700
                Re: Compare two methods of random permutations "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2013-05-16 06:10 +0100
                Re: Compare two methods of random permutations pacman@kosh.dhis.org (Alan Curry) - 2013-05-16 06:57 +0000
                Re: Compare two methods of random permutations "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2013-05-16 09:26 +0100
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-16 01:35 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-17 14:11 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-17 08:13 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 11:06 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 03:14 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 13:26 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 04:59 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 14:13 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 05:52 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 15:06 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 06:50 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 16:14 +0200
                Re: Compare two methods of random permutations James Dow Allen <jdallen2000@yahoo.com> - 2013-05-19 08:11 -0700
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 17:15 +0200
                Re: Compare two methods of random permutations Mok-Kong Shen <mok-kong.shen@t-online.de> - 2013-05-19 17:24 +0200

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