Re: 64 bit code

From	"BartC" <bc@freeuk.com>
Newsgroups	comp.programming
Subject	Re: 64 bit code
Date	2012-10-12 21:30 +0100
Organization	A noiseless patient Spider
Message-ID	<k59un2$qem$1@dont-email.me> (permalink)
References	(1 earlier) <507595db$0$6898$e4fe514c@news2.news.xs4all.nl> <k5488o$cbv$1@dont-email.me> <k54j49$cns$1@speranza.aioe.org> <162dnU-Rw5IpVOrNnZ2dnUVZ8qCdnZ2d@bt.com> <k59snb$oqm$1@speranza.aioe.org>

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"Rui Maciel" <rui.maciel@gmail.com> wrote in message
news:k59snb$oqm$1@speranza.aioe.org...
> Chris Uppal wrote:
>
>> Rui Maciel wrote:
>>
>>> And let's not forget about the ever elusive 80-bit extended precision
>>> floating point format, also known as "why bother".
>>
>> For one answer, people might like to read:
>>
>> http://www.cs.berkeley.edu/~wkahan/Stnfrd50.pdf

> In other words, in this example, Matrix A and vectors q and b generally
> are
> themselves the result of an approximate calculation, and their error isn't
> small. To put things in perspective, It's not uncommon for these errors to
> be in the 1%-0.1% range.  In some commercial number crunching applications
> that implement this class of methods, the error even goes up to 3%-4% in
> come applications.
>
> Meanwhile, discussing whether floats or doubles should be used is
> equivalent
> to discussing the significance of an error in the range of
> 0.0001%-0.00001%.
>
> Hence, why bother?

I didn't understand any of your argument. Using more precision is always
going to help some types of calculations. The difference between float and
double is a matter of 29 or so bits, about 500 million times more precision,
not the 10 to 100 million your figures suggest.

And the real reason for 80 bits, is probably that the mantissa is exactly 64
bits; that makes it attractive for the same sorts of reasons that 64-bit
processors are more popular than 52-bit ones. An 80-bit floating-point value 
can also represent a 64-bit integer exactly (signed *or* unsigned I 
believe). It's worth bothering with!

-- 
Bartc

Thread

64 bit code bob <bob@coolfone.comze.com> - 2012-10-10 08:22 -0700
  Re: 64 bit code Jongware <jongware@no-spam.plz> - 2012-10-10 17:35 +0200
    Re: 64 bit code "BartC" <bc@freeuk.com> - 2012-10-10 17:37 +0100
      Re: 64 bit code Robert Wessel <robertwessel2@yahoo.com> - 2012-10-10 12:54 -0500
      Re: 64 bit code Fritz Wuehler <fritz@spamexpire-201210.rodent.frell.theremailer.net> - 2012-10-10 21:37 +0200
        Re: 64 bit code BGB <cr88192@hotmail.com> - 2012-10-10 21:46 -0500
      Re: 64 bit code Rui Maciel <rui.maciel@gmail.com> - 2012-10-10 20:43 +0100
        Re: 64 bit code "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-10-12 08:40 +0100
          Re: 64 bit code BGB <cr88192@hotmail.com> - 2012-10-12 12:36 -0500
          Re: 64 bit code Rui Maciel <rui.maciel@gmail.com> - 2012-10-12 20:57 +0100
            Re: 64 bit code "BartC" <bc@freeuk.com> - 2012-10-12 21:30 +0100
              Re: 64 bit code BGB <cr88192@hotmail.com> - 2012-10-12 16:33 -0500
                Re: 64 bit code "BartC" <bc@freeuk.com> - 2012-10-13 00:44 +0100
                Re: 64 bit code Ben Pfaff <blp@cs.stanford.edu> - 2012-10-12 20:07 -0700
              Re: 64 bit code Rui Maciel <rui.maciel@gmail.com> - 2012-10-13 11:11 +0100
                Re: 64 bit code "BartC" <bc@freeuk.com> - 2012-10-13 13:11 +0100
                Re: 64 bit code Willem <willem@turtle.stack.nl> - 2012-10-13 12:34 +0000
                Re: 64 bit code BGB <cr88192@hotmail.com> - 2012-10-13 09:50 -0500
                Re: 64 bit code "BartC" <bc@freeuk.com> - 2012-10-13 17:25 +0100
                Re: 64 bit code Rui Maciel <rui.maciel@gmail.com> - 2012-10-13 17:53 +0100
                Re: 64 bit code Rui Maciel <rui.maciel@gmail.com> - 2012-10-13 17:05 +0100
          Re: 64 bit code "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-10-13 10:37 +0200
            Re: 64 bit code "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-10-27 12:18 +0100
              Re: 64 bit code "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-10-27 12:54 +0100
              Re: 64 bit code "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-10-27 15:13 +0200
                Re: 64 bit code Robert Miles <milesrf@Usenet-News.net> - 2012-10-28 04:12 -0500
                Re: 64 bit code "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-10-28 13:10 +0100
                Re: 64 bit code "LudovicoVan" <julio@diegidio.name> - 2012-10-29 04:38 +0000
                Re: 64 bit code "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-10-29 09:30 +0100
                Re: 64 bit code "LudovicoVan" <julio@diegidio.name> - 2012-10-30 22:09 +0000
                Re: 64 bit code "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-10-31 09:47 +0100
                Re: 64 bit code "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-10-31 09:55 +0100
                Re: 64 bit code "LudovicoVan" <julio@diegidio.name> - 2012-10-31 14:32 +0000
            Re: 64 bit code Patricia Shanahan <pats@acm.org> - 2012-10-27 08:51 -0700
              Re: 64 bit code "LudovicoVan" <julio@diegidio.name> - 2012-10-27 17:23 +0100
              Re: 64 bit code "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-10-27 20:43 +0200
                Re: 64 bit code "LudovicoVan" <julio@diegidio.name> - 2012-10-30 22:16 +0000
                Re: 64 bit code "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2012-10-31 09:53 +0100
                Re: 64 bit code "LudovicoVan" <julio@diegidio.name> - 2012-10-31 14:33 +0000
                Re: 64 bit code Fritz Wuehler <fritz@spamexpire-201211.rodent.frell.theremailer.net> - 2012-11-01 00:25 +0100
      Re: 64 bit code Rui Maciel <rui.maciel@gmail.com> - 2012-10-10 21:04 +0100
        Re: 64 bit code "BartC" <bc@freeuk.com> - 2012-10-10 21:52 +0100
          Re: 64 bit code Ian Collins <ian-news@hotmail.com> - 2012-10-11 10:50 +1300
            Re: 64 bit code BGB <cr88192@hotmail.com> - 2012-10-10 21:54 -0500
              Re: 64 bit code "BartC" <bc@freeuk.com> - 2012-10-11 13:11 +0100
                Re: 64 bit code BGB <cr88192@hotmail.com> - 2012-10-11 11:17 -0500
      Re: 64 bit code Ben Pfaff <blp@cs.stanford.edu> - 2012-10-10 13:17 -0700
        Re: 64 bit code Fritz Wuehler <fritz@spamexpire-201210.rodent.frell.theremailer.net> - 2012-10-11 19:36 +0200
          Re: 64 bit code Ben Pfaff <blp@cs.stanford.edu> - 2012-10-12 08:13 -0700
    Re: 64 bit code Rui Maciel <rui.maciel@gmail.com> - 2012-10-10 20:38 +0100
    Re: 64 bit code Robin Vowels <robin.vowels@gmail.com> - 2012-10-10 15:22 -0700
  Re: 64 bit code Robert Miles <milesrf@Usenet-News.net> - 2012-10-12 02:13 -0500

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