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Groups > comp.lang.c > #139152
| Subject | Re: Range-aware modulo operator -% |
|---|---|
| Newsgroups | comp.lang.c, comp.lang.c++ |
| References | <q040h4$bie$1@dont-email.me> |
| From | Richard Damon <Richard@Damon-Family.org> |
| Message-ID | <FYfVD.40401$ec.37607@fx26.iad> (permalink) |
| Organization | Forte - www.forteinc.com |
| Date | 2018-12-27 21:34 -0500 |
Cross-posted to 2 groups.
On 12/27/18 9:09 PM, 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.
>
> Just sayin'... :-)
>
It used to be that an implementation was allowed to define -1 % 10 to be
9, but they standard changed the rule for division so that that wasn't
allowed anymore. (It required -1/10 == -1)
The key fact is that given i, j, m, n as integral types and no overflow
occurring.
If i = m / n and j = m % n
then i * n + j == m
for j to always be positive, i needs to be the floor of the division,
not from round to 0.
The key to remember is that % is NOT the modulus operator, but the
remainder operator (which work the same for positive numbers).
It is simple enough to define a mod function that gets the results you
want, so not that much need for a new operator.
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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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