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Re: Best search algorithm to find a condition within a range.

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From Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups comp.lang.javascript
Subject Re: Best search algorithm to find a condition within a range.
Date Fri, 10 Apr 2015 00:02:27 +0100
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Dr J R Stockton <reply1500@merlyn.demon.co.uk.invalid> writes:

> In comp.lang.javascript message <878ue3zrws.fsf@bsb.me.uk>, Tue, 7 Apr
> 2015 19:58:59, Ben Bacarisse <ben.usenet@bsb.me.uk> posted:
>
>>If, however, you only want to find the leading digit, there may be a
>>better way, but it's likely to use logarithms:
>>
>>  log(3243787...54395)/log(4294967295) = 8.15..
>>  floor(3243787...54395 / 4294967295^8) = 28
>
>
> It seems probable that, with real rather than integer arithmetic, there
> will be at least one case in which the small errors in the division and
> logarithms will put the value on the wrong side of an integer, in the
> opinion of float.
>
> So either one must test all possible cases or do some rather difficult
> reasoning to prove that it always works correctly, or accept the risk of
> occasional error.

Yes, it's not hard to test both possible powers so the occasional error
hardly matters.  In fact, one might even use a very crude log function
(maybe just take the digit length?), accept the ensuing errors, and test
the possible powers.

BTW, I make not claim that this is of any value (I can't see how it
could be, really) just that it's a way to do what the OP (incorrectly,
in my option) claimed to want.

<snip>
-- 
Ben.

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Thread

Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 02:43 -0700
  Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-07 13:07 +0200
    Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 04:38 -0700
      Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 04:48 -0700
      Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-07 14:49 +0200
  Re: Best search algorithm to find a condition within a range. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-07 13:27 +0100
    Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 06:04 -0700
      Re: Best search algorithm to find a condition within a range. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-07 14:23 +0100
        Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 06:54 -0700
          Re: Best search algorithm to find a condition within a range. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-07 16:31 +0100
            Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 08:59 -0700
              Re: Best search algorithm to find a condition within a range. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-07 19:58 +0100
                Re: Best search algorithm to find a condition within a range. Dr J R Stockton <reply1500@merlyn.demon.co.uk.invalid> - 2015-04-09 23:08 +0100
                Re: Best search algorithm to find a condition within a range. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-10 00:02 +0100
            Re: Best search algorithm to find a condition within a range. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-04-07 18:37 +0200
              Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 09:55 -0700
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-07 20:30 +0200
                Re: Best search algorithm to find a condition within a range. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-04-07 20:58 +0200
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-07 22:19 +0200
                Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-08 00:14 -0700
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-08 10:55 +0200
                Re: Best search algorithm to find a condition within a range. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-04-09 13:03 +0200
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-09 14:11 +0200
                Re: Best search algorithm to find a condition within a range. "Christoph M. Becker" <cmbecker69@arcor.de> - 2015-04-09 14:55 +0200
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-09 15:20 +0200
                Re: Best search algorithm to find a condition within a range. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-09 14:49 +0100
                Re: Best search algorithm to find a condition within a range. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-04-09 16:10 +0200
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-09 16:17 +0200
                Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-09 07:22 -0700
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-09 16:44 +0200
                Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-09 07:57 -0700
                Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-09 08:05 -0700
                Re: Best search algorithm to find a condition within a range. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-09 17:04 +0100
                Re: Best search algorithm to find a condition within a range. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-04-09 16:14 +0200
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-09 16:34 +0200
                Re: Best search algorithm to find a condition within a range. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-04-09 17:39 +0200
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-09 18:04 +0200
                Re: Best search algorithm to find a condition within a range. Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-04-09 18:26 +0200
                Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-09 22:13 +0200
              Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 10:00 -0700
    Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 06:16 -0700
      Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-07 15:28 +0200
        Re: Best search algorithm to find a condition within a range. jonas.thornvall@gmail.com - 2015-04-07 06:58 -0700
          Re: Best search algorithm to find a condition within a range. "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-04-07 20:25 +0200
      Re: Best search algorithm to find a condition within a range. Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-04-07 14:33 +0100

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