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Groups > comp.lang.c > #139161
| Subject | Re: Range-aware modulo operator -% |
|---|---|
| Newsgroups | comp.lang.c, comp.lang.c++ |
| References | <q040h4$bie$1@dont-email.me> |
| From | Bart <bc@freeuk.com> |
| Message-ID | <tGoVD.88490$Ck1.46277@fx18.am4> (permalink) |
| Organization | virginmedia.com |
| Date | 2018-12-28 12:29 +0000 |
Cross-posted to 2 groups.
On 28/12/2018 02:09, Rick C. Hodgin wrote:
> I think C/C++ needs to have a range-aware modulo operator that will
> continue ranging properly when it encounters negative values.
>
> We have this:
> i = (i + 1) % 10; // Always ranges 0..9
>
> But what if you try this when i = 0:
> i = (i - 1) % 10;
>
> It won't produce the same result in the same pattern seen when you
> started at a positive i and tended toward 0. It begins a new trend,
> one which is useful, but not always desirable.
>
> A range-aware modulo operator would know that it should always be
> in the range 0..9 (from the example above), and also that it should
> continue the pattern seen in the positive integers, such that when
> given a negative input value, it handles the processing differently:
>
> // v=value, m=modulo number
> int range_modulo(int v, int m)
> {
> if (v >= 0) return (v % m);
> else return ((m + (v % m)) % m);
> }
>
> int i;
> for (i = 12; i >= -12; --i)
> printf("%d --> mod 10 = %d\n", i, range_modulo(i, 10));
>
> -----
> I propose the -% symbol for the operator.
>
> It would allow things that are sometimes needed in video games,
> as just one example, when a player hits the left button instead
> of the right button, and you need it to go the other way, AND you
> want it to just work while using the same math.
I used this loop to better show the differences:
for (i = 12; i >= -12; --i) {
if (i==0) puts("");
printf("rmod(%3d,10) = %3d, %3d%%10 = %3d\n", i,
range_modulo(i, 10),i,i%10);
if (i==0) puts("");
}
The % operator [which in my language is called 'rem'] shows symmetrical
behaviour around zero, while your range_modulo doesn't.
Both behaviours are useful for different purposes. But the simplest
thing to do is to just keep it as a function, as like that it will work
/now/ on a hundred compilers.
"-%" is unlikely to ever work on any. Apart from which, there's already
enough confusion as to exactly what "%" does, let alone "-%", especially
with the /four/ combinations of negative operands.
(Note that when m is negative, eg. i/(-10), then both appear to have the
same behaviour. The modulo nature of your range_modulo disappears. You
may wish to use abs(m) inside that function, and perhaps re-apply the
sign to the result, if that is important.)
--
bart
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Range-aware modulo operator -% "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2018-12-27 21:09 -0500
Re: Range-aware modulo operator -% Richard Damon <Richard@Damon-Family.org> - 2018-12-27 21:34 -0500
Re: Range-aware modulo operator -% "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2018-12-28 05:37 +0100
Re: Range-aware modulo operator -% James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-12-29 16:04 -0500
Re: Range-aware modulo operator -% Richard Damon <Richard@Damon-Family.org> - 2018-12-29 19:13 -0500
Re: Range-aware modulo operator -% Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-12-28 03:05 +0000
Re: Range-aware modulo operator -% Robert Wessel <robertwessel2@yahoo.com> - 2018-12-27 21:31 -0600
Re: Range-aware modulo operator -% Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-12-28 04:20 +0000
Re: Range-aware modulo operator -% James Kuyper <jameskuyper@alumni.caltech.edu> - 2018-12-27 19:32 -0800
Re: Range-aware modulo operator -% Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-12-28 04:18 +0000
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2018-12-28 12:29 +0000
Re: Range-aware modulo operator -% "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2018-12-28 08:10 -0500
Re: Range-aware modulo operator -% Richard Damon <Richard@Damon-Family.org> - 2018-12-28 10:25 -0500
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2018-12-28 15:56 +0000
Re: Range-aware modulo operator -% Richard Damon <Richard@Damon-Family.org> - 2018-12-28 17:26 -0500
Re: Range-aware modulo operator -% Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> - 2018-12-28 23:45 +0100
Re: Range-aware modulo operator -% "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2018-12-28 11:44 -0500
Re: Range-aware modulo operator -% "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2018-12-28 12:16 -0500
Re: Range-aware modulo operator -% Richard Damon <Richard@Damon-Family.org> - 2018-12-28 17:08 -0500
Re: Range-aware modulo operator -% Tim Rentsch <txr@alumni.caltech.edu> - 2018-12-28 15:01 -0800
Re: Range-aware modulo operator -% "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2018-12-31 09:04 -0500
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2018-12-31 18:07 +0000
Re: Range-aware modulo operator -% "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2018-12-31 14:22 -0500
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2018-12-31 21:05 +0000
Re: Range-aware modulo operator -% "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2018-12-31 16:32 -0500
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2018-12-31 23:43 +0000
Re: Range-aware modulo operator -% Keith Thompson <kst-u@mib.org> - 2018-12-31 16:44 -0800
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2019-01-01 01:06 +0000
Re: Range-aware modulo operator -% Keith Thompson <kst-u@mib.org> - 2018-12-31 19:06 -0800
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2019-01-01 11:32 +0000
Re: Range-aware modulo operator -% Keith Thompson <kst-u@mib.org> - 2019-01-01 12:48 -0800
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2019-01-01 23:54 +0000
Re: Range-aware modulo operator -% Keith Thompson <kst-u@mib.org> - 2019-01-01 16:09 -0800
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2019-01-02 00:49 +0000
Re: Range-aware modulo operator -% Keith Thompson <kst-u@mib.org> - 2019-01-01 17:53 -0800
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2019-01-02 02:36 +0000
Leader Kiki is not going to like this... (Was: Range-aware modulo operator -%) gazelle@shell.xmission.com (Kenny McCormack) - 2019-01-02 08:36 +0000
Re: Range-aware modulo operator -% Keith Thompson <kst-u@mib.org> - 2019-01-02 00:38 -0800
Re: Range-aware modulo operator -% rbowman <bowman@montana.com> - 2019-01-01 22:40 -0700
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2019-01-02 12:12 +0000
Re: Range-aware modulo operator -% gazelle@shell.xmission.com (Kenny McCormack) - 2019-01-01 01:53 +0000
Re: Range-aware modulo operator -% Richard Damon <Richard@Damon-Family.org> - 2018-12-31 16:57 -0500
Re: Range-aware modulo operator -% Bart <bc@freeuk.com> - 2018-12-31 22:33 +0000
Re: Range-aware modulo operator -% Keith Thompson <kst-u@mib.org> - 2018-12-31 13:34 -0800
Re: Range-aware modulo operator -% Richard Damon <Richard@Damon-Family.org> - 2018-12-31 16:43 -0500
Re: Range-aware modulo operator -% Keith Thompson <kst-u@mib.org> - 2018-12-31 15:20 -0800
Re: Range-aware modulo operator -% Eduardo <abdulai60@gmail.com> - 2018-12-28 07:18 -0800
Re: Range-aware modulo operator -% "Rick C. Hodgin" <rick.c.hodgin@gmail.com> - 2018-12-28 11:45 -0500
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