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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 Tue, 07 Apr 2015 19:58:59 +0100
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jonas.thornvall@gmail.com writes:

> Den tisdag 7 april 2015 kl. 17:31:49 UTC+2 skrev Ben Bacarisse:
>> jonas.thornvall@gmail.com writes:
>> 
>> > Den tisdag 7 april 2015 kl. 15:23:47 UTC+2 skrev Ben Bacarisse:
>> >> jonas.thornvall@gmail.com writes:
>> <snip>
>> >> > I aim to replace the slow add when dealing with real big bases with a
>> >> > search.  
>> >> 
>> >> I thought your post was about converting between bases.  If it wasn't,
>> >> just ignore my comments.
>> >
>> > It is about converting bases as fast as possible in a general way that
>> > work for anybase no matter how ***big***. That mean you cannot add up
>> > digits, it is to slow you have to search the digit, doing a binary
>> > search or something better.
>> 
>> Then my point stands.  Why are you "searching" for a digit rather than
>> simply calculating it?  Have you determined that the usual method is too
>> slow and you have some alternative in mind?
>
> Yes the binary search have better time than linear add.
>
> Example base 4294967295

That's a very odd base to use.  4294967296 would, on the other hand, be
quite a reasonable choice in some contexts.  Not for ECMAScript, though,
because, in general, the best base to use is the largest one where you
can get an exact product of two digits from the underlying programming
environment.

> number =
> 3243787983738733984329847327432738783449058438543890486865659065465474857454395
>
> Find value of first digitplace (higest), using commaseparated notation
> it will be a value between 1 and (4294967295-1)

It's 28.

If you want to represent that number in the specified base, you should
just generate the digits as normal -- taking the remainder and
dividing.  You have invented a problem that can be avoided altogether if
you choose not to find the most significant digit first.

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

-- 
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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