Re: Another little puzzle

From	"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups	comp.programming
Subject	Re: Another little puzzle
Date	2022-12-14 16:41 +0100
Organization	Aioe.org NNTP Server
Message-ID	<tncqs4$uoe$1@gioia.aioe.org> (permalink)
References	(2 earlier) <tnci0u$2of9h$3@dont-email.me> <tncjem$19kh$1@gioia.aioe.org> <tnclg3$2of9o$2@dont-email.me> <tncob5$1oat$1@gioia.aioe.org> <tncpgk$2of9h$7@dont-email.me>

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On 2022-12-14 16:18, Richard Heathfield wrote:

>> BTW, averaging floats is a nasty problem too. A naive implementation 
>> quickly loses precision.
> 
> We're dealing with 'o'clock' and "HH:MM", and nowadays we have 64-bit 
> integer types and there are even 128-bit integers mooching around 
> looking for a reason to exist. You'd have to average a hell of a lot of 
> times even to /need/ floats, let alone lose significant precision.

I never suggested float for averaging time stamps, I pointed out that 
averaging is not a simple problem. E.g. try this one:

    function Average (X : Float; N : Positive) return Float is
       Sum : Float := 0.0;
    begin
       for Index in 1..N loop
          Sum := Sum + X;
       end loop;
       return Sum / Float (N);
    end Average;

The function does naive averaging. For simplicity it just sums up the 
same number X N times and divides by N.

    Average (1.0, 17_000_000)  = 0.986895
    Average (1.0, 100_000_000) = 0.167772
    Average (1.0, 200_000_000) = 0.838861

The issue is catastrophic precision loss of addition Sum + X when Sum >> X.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

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Re: Another little puzzle "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2022-12-14 14:06 +0100
  Re: Another little puzzle Richard Heathfield <rjh@cpax.org.uk> - 2022-12-14 13:10 +0000
    Re: Another little puzzle "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2022-12-14 14:35 +0100
      Re: Another little puzzle Richard Heathfield <rjh@cpax.org.uk> - 2022-12-14 14:10 +0000
        Re: Another little puzzle "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2022-12-14 15:58 +0100
          Re: Another little puzzle Richard Heathfield <rjh@cpax.org.uk> - 2022-12-14 15:18 +0000
            Re: Another little puzzle "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2022-12-14 16:41 +0100
              Re: Another little puzzle "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> - 2022-12-14 16:43 +0100
                Re: Another little puzzle Y A <angel00000100000@mail.ee> - 2023-01-09 16:33 -0800
              Re: Another little puzzle Richard Heathfield <rjh@cpax.org.uk> - 2022-12-14 16:13 +0000
        Re: Another little puzzle V <angleeeeeeee@mail.ee> - 2023-05-10 11:16 -0700
    Re: Another little puzzle Ǝ <angel0000000001000000000000@mail.ee> - 2022-12-30 05:59 -0800

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