Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.c > #402447
| From | bart <bc@freeuk.com> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: official library of tiny functions lacking in c |
| Date | 2026-09-28 11:43 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <119dgc1$28if0$1@dont-email.me> (permalink) |
| References | <119ajku$15pve$1@dont-email.me> <119blrr$1ka68$1@dont-email.me> <119d2en$22to9$1@dont-email.me> |
On 28/09/2026 07:45, Lawrence D’Oliveiro wrote:
> On Sun, 27 Sep 2026 20:04:20 +0200, fir wrote:
>
>> float len2(float x,float y) { return sqrtf(x*x+y*y);}
>
> Interesting:
>
> /*
> Comparison of the naïve calculation of a triangle
> hypotenuse with the standard-library hypot(3) function.
> */
>
> #include <math.h>
> #include <values.h>
> #include <stdio.h>
>
> static float len2(float x,float y) { return sqrtf(x*x+y*y);}
>
> static void compare_for
> (
> float x
> )
> {
> fprintf
> (
> stdout,
> "for %.7e: len2 = %.7e, hypot = %.7e\n",
> x, len2(x, x), hypotf(x, x)
> );
> } /*compare_for*/
This is a diabolic layout. I had to fix so that I can see what it was doing.
How can you stretch a one-line function to this length?!
> int main(void)
> {
> compare_for(FLT_MAX / 2.0f);
> compare_for(2.0 / FLT_MAX);
> return
> 0;
> } /*main*/
>
> Output:
>
> ldo@theon:c_try> !./
> ./naive_hypot
> for 1.7014117e+38: len2 = inf, hypot = 2.4061594e+38
> for 5.8774718e-39: len2 = 0.0000000e+00, hypot = 8.3120008e-39
> ldo@theon:c_try>
>
> How is it the standard library function is able to produce a
> reasonable-looking result where your function breaks down?
You mean a reasonable looking result for quite unreasonable inputs?
Because it's common to work with triangles whose sides are
170141173319264429905852091742258462720 units long!
The simple function squares its arguments, so the upper limit for first
test would be sqrt(FLT_MAX)/2.0 (since it also adds the two squares).
In that case both versions give the same result. For second test, where
you are working with triangles with non-zero sides smaller than
Plancks's Constant, I haven't dealt with.
Sure, the official version can deal with a wider range, but try it with
FLT_MAX and both fail.
In practice, for inputs this huge, it makes sense to switch to 'double'.
Then it will also work better for arbitrary expressions that happen to
use squares and other powers.
So I think this overhead for 'hypot' is pointless, given that, in
general, for any 'x' or type float, then x*x /anywhere in a program/
will overflow when x is bigger than sqrt(FLT_MAX).
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll 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
csiph-web