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Re: Fixed-point arithmetic library

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On Thu, 23 Feb 2012 21:16:04 +0000, Tom Anderson
<twic@urchin.earth.li> wrote:

>On Wed, 22 Feb 2012, Gene Wirchenko wrote:

[snip]

>>     I have been working with fixed-point arithmetic in JavaScript so
>> that I can add dollar amounts exactly.  Maybe OP has something similar
>> in mind, though with the number of digits of precision that he wants
>> before the decimal point, I hope it is not currency-related.
>
>It is currency-related. What's wrong with that?

     You are dealing with monstrously-large numbers.  National debts
or something similar?

     If you only needed up to fifteen digits of precision total, you
could use IEEE 754 64-bit floating point format and store integers.
They will be stored exactly.  IEEE 754 is the only number format that
JavaScript exposes for variable types (though it does use 32-bit
integers internally on some operations).

     I had to experiment with this, but I got it working.

     Looking up further, according to Wikipedia, there is a 128-bit
format that has 34.02 digits of precision.  If your target language
has this format as one of its number types, you could store integers
in such variables.  You did state that you need 30 digits of
precision, so this would fit.  This would be a cheap, fairly simple
solution.

Sincerely,

Gene Wirchenko

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Fixed-point arithmetic library Tom Anderson <twic@urchin.earth.li> - 2012-02-22 21:39 +0000
  Re: Fixed-point arithmetic library Jan Burse <janburse@fastmail.fm> - 2012-02-22 22:59 +0100
    Re: Fixed-point arithmetic library Tom Anderson <twic@urchin.earth.li> - 2012-02-23 21:15 +0000
      Re: Fixed-point arithmetic library markspace <-@.> - 2012-02-23 13:53 -0800
      Re: Fixed-point arithmetic library Robert Klemme <shortcutter@googlemail.com> - 2012-02-23 23:21 +0100
      Re: Fixed-point arithmetic library Jan Burse <janburse@fastmail.fm> - 2012-02-24 00:02 +0100
  Re: Fixed-point arithmetic library Robert Klemme <shortcutter@googlemail.com> - 2012-02-22 23:13 +0100
    Re: Fixed-point arithmetic library Gene Wirchenko <genew@ocis.net> - 2012-02-22 14:59 -0800
      Re: Fixed-point arithmetic library Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-23 01:05 +0000
        Re: Fixed-point arithmetic library Tom Anderson <twic@urchin.earth.li> - 2012-02-23 21:21 +0000
          Re: Fixed-point arithmetic library Gene Wirchenko <genew@ocis.net> - 2012-02-23 13:49 -0800
      Re: Fixed-point arithmetic library Tom Anderson <twic@urchin.earth.li> - 2012-02-23 21:16 +0000
        Re: Fixed-point arithmetic library Gene Wirchenko <genew@ocis.net> - 2012-02-23 14:03 -0800
          Re: Fixed-point arithmetic library Lew <noone@lewscanon.com> - 2012-02-23 14:42 -0800
            Re: Fixed-point arithmetic library Gene Wirchenko <genew@ocis.net> - 2012-02-23 15:08 -0800
        Re: Fixed-point arithmetic library Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-23 23:05 +0000
    Re: Fixed-point arithmetic library glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-02-27 00:59 +0000
      Re: Fixed-point arithmetic library Arne Vajhøj <arne@vajhoej.dk> - 2012-02-26 20:50 -0500
        Re: Fixed-point arithmetic library Robert Klemme <shortcutter@googlemail.com> - 2012-02-27 07:32 +0100
          Re: Fixed-point arithmetic library Jan Burse <janburse@fastmail.fm> - 2012-02-27 13:46 +0100
  Re: Fixed-point arithmetic library Roedy Green <see_website@mindprod.com.invalid> - 2012-02-24 16:26 -0800

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