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Re: There is no "correct" result for std::fmod across all IEEE 754 representations

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On 3/2/25 04:07, Michael S wrote:
> On Sat, 01 Mar 2025 21:57:13 +0000
> Mr Flibble <leigh@i42.co.uk> wrote:
...
>> My point is std::fmod is almost useless
>> MATHEMATICALLY unless the arguments don't involve approximation, but
>> with IEEE 754 floating point you get what you pay for.
>>
>> /Flibble
>
> If you were saying that fmod(x/y) for big values of x/y is almost

fmod(x,y)?

> useless physically / engineerially then I'd tend to agree.
> When physicist or engineer says 'double x= bar;' where bar is a number
> that can be represented exactly in binary64 then what he means (if he
> cared at all to think about what he means, which is rare) is that he
> believes that x is in range (bar-ULP:bar+ULP] and he hopes that
> probability of x being within range [bar-ULP/2:bar+ULP/2] is much
> higher that 0.5. So, obviously, as long as y is abs(y)<ULP(x) for
> physicist fmod(x/y) is meaningless.

Actually, most numbers of relevance to science and engineering have a
uncertainty which is determined by how the raw measurements were made
from which the number was calculated, which are usually much bigger than
1 ULP. The only exceptions are mathematical constants. Despite that
fact, it is in fact quite commonplace for the uncertainties to be small
enough to make the return value of fmod() meaningful. As a general rule,
if that weren't the case, there wouldn't be any desire to use fmod().

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There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-01 19:27 +0000
  Re: There is no "correct" result for std::fmod across all IEEE 754 representations Michael S <already5chosen@yahoo.com> - 2025-03-01 23:03 +0200
    Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-01 21:57 +0000
      Re: There is no "correct" result for std::fmod across all IEEE 754 representations Michael S <already5chosen@yahoo.com> - 2025-03-02 11:07 +0200
        Re: There is no "correct" result for std::fmod across all IEEE 754 Muttley@DastardlyHQ.org - 2025-03-02 09:17 +0000
          Re: There is no "correct" result for std::fmod across all IEEE 754 Michael S <already5chosen@yahoo.com> - 2025-03-02 16:03 +0200
            Re: There is no "correct" result for std::fmod across all IEEE 754 Muttley@dastardlyhq.com - 2025-03-02 16:56 +0000
        Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-02 15:24 +0000
        Re: There is no "correct" result for std::fmod across all IEEE 754 representations James Kuyper <jameskuyper@alumni.caltech.edu> - 2025-03-02 17:37 -0500
          Re: There is no "correct" result for std::fmod across all IEEE 754 representations Michael S <already5chosen@yahoo.com> - 2025-03-03 13:20 +0200
  Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 16:25 +0100
    Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 16:30 +0100
      Re: There is no "correct" result for std::fmod across all IEEE 754 representations Michael S <already5chosen@yahoo.com> - 2025-03-03 18:54 +0200
    Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 17:11 +0000
      Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 18:26 +0100
        Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 18:20 +0000
          Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 19:26 +0100
            Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 18:33 +0000
              Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 19:37 +0100
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 18:46 +0000
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 19:48 +0100
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 18:50 +0000
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 19:53 +0100
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 18:58 +0000
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 20:05 +0100
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 19:09 +0000
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 20:14 +0100
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 20:27 +0100
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 19:33 +0000
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-03 20:36 +0100
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-03 19:37 +0000
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Bonita Montero <Bonita.Montero@gmail.com> - 2025-03-04 10:42 +0100
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations Mr Flibble <leigh@i42.co.uk> - 2025-03-04 18:24 +0000
                Re: There is no "correct" result for std::fmod across all IEEE 754 representations "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-03-03 12:25 -0800

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