Re: official library of tiny functions lacking in c

From	bart <bc@freeuk.com>
Newsgroups	comp.lang.c
Subject	Re: official library of tiny functions lacking in c
Date	2026-09-28 16:40 +0100
Organization	A noiseless patient Spider
Message-ID	<119e1ok$2fheo$1@dont-email.me> (permalink)
References	(3 earlier) <119c14p$1ohra$1@dont-email.me> <119ca96$1sr2q$1@dont-email.me> <119d88u$23bo0$2@dont-email.me> <119dgg0$28if0$2@dont-email.me> <119e0ak$2es7t$1@dont-email.me>

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On 28/09/2026 16:15, James Kuyper wrote:
> On 28/09/2026 12:45, bart wrote:
>> On 28/09/2026 09:25, David Brown wrote:
> ...>> It also has a "hypot" function that returns, approximately,
> sqrt(x*x +
>>> y*y).
> ...> So why was hypot() ever added? Somebody thought it was a good idea at
>> one time to add a such a one-line function?
> It was part of the major expansion to the <math.h> library that occurred
> in C99. It was added because of the "without undue overflow or
> underflow." requirement. Achieving that result makes it a bit more
> complicated than just a one-line function. Also, even most people who
> are well aware of that problem are unaware of how best to avoid it. See
> <https://en.wikipedia.org/wiki/Pythagorean_addition#Calculation_order>
> for more details.

I think most will be vaguely aware of such problems, but usually they 
don't matter because they only happen with unlikely, extreme inputs.

One simple way around in this case, is to use 64-bit floats for the 
calculation, even if the inputs are 32-bits.

That might kick the can down the road enough that overflows will 
virtually never occur (eg. it might need inputs over 10**150, and that I 
think is impossible if inputs were promoted from 32 bits).

I'm less familiar with underflows, ie. values smaller than around 
10e-308, but I think the same applies.

The technique demonstrated in LD'O's post I think buys you one more bit 
of exponent range (although the article you linked to seems to suggest 
you can go beyond that with extra scaling).

When such things used to be important to me, I tried to avoid doing the 
square-root part anyway, for example I would compare one set of x*x + 
y*y with another. In that case it is necessary to express the full 
magnitude.

If the values represent length, then another approach would be a choice 
of units. I liked using mm, but if expressed in metres, then I think 
that's another 10 extra bits of binary exponent range, unless the issue 
is underflow, then it might make it worse!

In any case, it was NEVER a problem (well, until someone zoomed in 
enough within my CAD product that they hit the limitations of the 
floating point representation. Things would get jerky).

Thread

official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-27 10:20 +0200
  Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-27 20:04 +0200
    Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-27 21:38 +0100
      Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-27 23:16 +0200
        Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-28 00:53 +0100
          Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-28 04:31 +0200
          Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-28 10:25 +0200
            Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-28 11:45 +0100
              Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-28 13:56 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-28 14:38 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-28 16:12 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-28 16:52 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-28 18:49 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-28 20:26 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-29 09:45 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-29 12:54 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-29 15:56 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-29 18:15 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-29 20:24 +0200
                Re: official library of tiny functions lacking in c scott@slp53.sl.home (Scott Lurndal) - 2026-09-29 19:41 +0000
                Re: official library of tiny functions lacking in c cross@spitfire.i.gajendra.net (Dan Cross) - 2026-09-29 21:37 +0000
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 01:33 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-30 09:28 +0200
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 13:41 +0300
                Re: official library of tiny functions lacking in c Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-01 07:25 -0700
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-10-01 17:50 +0300
                Re: official library of tiny functions lacking in c Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-01 09:37 -0700
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 01:19 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-30 09:44 +0200
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-29 16:01 +0200
                Re: official library of tiny functions lacking in c "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-09-30 01:00 -0700
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-30 13:01 +0200
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-10-01 08:52 +0000
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-30 01:56 +0000
                Re: official library of tiny functions lacking in c Tim Rentsch <tr.17687@z991.linuxsc.com> - 2026-10-01 07:15 -0700
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-29 09:28 +0200
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 07:10 +0000
                Re: official library of tiny functions lacking in c "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-09-28 15:30 -0700
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-29 09:03 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-29 11:11 +0100
                Re: official library of tiny functions lacking in c scott@slp53.sl.home (Scott Lurndal) - 2026-09-29 14:38 +0000
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-30 07:02 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 11:35 +0100
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-30 14:14 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 13:45 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-30 15:30 +0200
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 17:14 +0300
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-30 16:42 +0200
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 18:02 +0300
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 16:54 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-30 18:26 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 22:12 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-10-01 09:44 +0200
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-10-01 10:42 +0100
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-10-01 13:50 +0300
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-10-01 12:29 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-10-02 09:35 +0200
                Re: official library of tiny functions lacking in c Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-02 04:03 -0700
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-10-02 13:50 +0200
                Re: official library of tiny functions lacking in c Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-02 11:22 -0700
                Re: official library of tiny functions lacking in c gazelle@shell.xmission.com (Kenny McCormack) - 2026-10-02 18:33 +0000
                Re: official library of tiny functions lacking in c scott@slp53.sl.home (Scott Lurndal) - 2026-10-03 14:30 +0000
                Re: official library of tiny functions lacking in c Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-10-03 16:37 -0700
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-10-01 13:29 +0200
                Re: official library of tiny functions lacking in c scott@slp53.sl.home (Scott Lurndal) - 2026-10-01 14:46 +0000
                Re: official library of tiny functions lacking in c "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-01 15:37 -0700
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-10-02 08:57 +0200
                Re: official library of tiny functions lacking in c "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-10-02 00:37 -0700
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 17:12 +0100
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 14:09 +0300
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-30 13:55 +0200
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-30 14:31 +0200
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 16:12 +0300
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-30 19:33 +0200
                Re: official library of tiny functions lacking in c scott@slp53.sl.home (Scott Lurndal) - 2026-09-30 18:14 +0000
                Re: official library of tiny functions lacking in c James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-01 08:34 -0400
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 07:08 +0000
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-29 15:02 +0100
                Re: official library of tiny functions lacking in c scott@slp53.sl.home (Scott Lurndal) - 2026-09-29 14:43 +0000
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-29 16:07 +0100
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 22:58 +0000
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 00:13 +0100
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-30 07:13 +0000
                Re: official library of tiny functions lacking in c Johann 'Myrkraverk' Oskarsson <johann@myrkraverk.invalid> - 2026-10-01 02:41 +0800
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 14:15 +0300
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 14:18 +0300
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 13:24 +0100
                Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-30 14:45 +0200
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 15:56 +0300
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-30 22:31 +0000
                Re: official library of tiny functions lacking in c Michael S <already5chosen@yahoo.com> - 2026-09-30 14:32 +0300
                Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-28 17:22 +0200
                Re: official library of tiny functions lacking in c Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2026-09-28 17:24 -0700
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-29 09:54 +0200
                Re: official library of tiny functions lacking in c "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-09-29 16:48 -0700
              Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-28 14:16 +0200
              Re: official library of tiny functions lacking in c James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-09-28 11:15 -0400
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-28 16:40 +0100
                Re: official library of tiny functions lacking in c "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-09-29 16:50 -0700
              Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 06:38 +0000
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-29 14:36 +0100
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 22:49 +0000
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-29 23:59 +0100
                Re: official library of tiny functions lacking in c "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-09-29 16:51 -0700
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-30 01:54 +0000
                Re: official library of tiny functions lacking in c James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-09-29 22:09 -0400
                Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-30 10:52 +0100
                Re: official library of tiny functions lacking in c David Brown <david.brown@hesbynett.no> - 2026-09-30 12:38 +0200
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-10-01 08:49 +0000
                Re: official library of tiny functions lacking in c James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-10-01 08:48 -0400
    Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-28 06:45 +0000
      Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-28 12:42 +0200
        Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 00:58 +0000
          Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-29 03:02 +0200
            Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 03:16 +0000
              Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-29 14:20 +0200
                Re: official library of tiny functions lacking in c Paul <nospam@needed.invalid> - 2026-09-29 12:39 -0400
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 22:50 +0000
                Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-30 02:57 +0200
                Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-30 02:00 +0000
                Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-30 10:08 +0200
                Re: official library of tiny functions lacking in c fir <profesor.fir@gmail.com> - 2026-09-30 13:58 +0200
      Re: official library of tiny functions lacking in c bart <bc@freeuk.com> - 2026-09-28 11:43 +0100
        Re: official library of tiny functions lacking in c Lawrence D’Oliveiro <ldo@nz.invalid> - 2026-09-29 01:00 +0000
        Re: official library of tiny functions lacking in c Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2026-09-30 07:59 +0200
      Re: official library of tiny functions lacking in c James Kuyper <jameskuyper@alumni.caltech.edu> - 2026-09-28 11:03 -0400
    Re: official library of tiny functions lacking in c NOTE fir <profesor.fir@gmail.com> - 2026-09-28 17:50 +0200
    Re: official library of tiny functions lacking in c "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2026-09-30 12:42 -0700
  Re: official library of tiny functions lacking in c tTh <tth@none.invalid> - 2026-09-28 00:02 +0200

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