Re: Range-aware modulo operator -%

Subject	Re: Range-aware modulo operator -%
Newsgroups	comp.lang.c
References	(16 earlier) <lny384kst5.fsf@kst-u.example.com> <65TWD.67453$Ab5.11301@fx04.am4> <lnlg43ly2p.fsf@kst-u.example.com> <WUTWD.86605$lN1.12840@fx13.am4> <lnftublt9t.fsf@kst-u.example.com>
From	Bart <bc@freeuk.com>
Message-ID	<0tVWD.263283$DWh1.99504@fx36.am4> (permalink)
Organization	virginmedia.com
Date	2019-01-02 02:36 +0000

Show all headers | View raw

On 02/01/2019 01:53, Keith Thompson wrote:
> Bart <bc@freeuk.com> writes:
>> On 02/01/2019 00:09, Keith Thompson wrote:
> [...]
>>> But I'm curious, do you understand the description in the standard?
>>> Did you even know what it said before I pointed it out?
>>
>> You mean 6.8.4.1p2? No I don't remember looking at it before.
> 
> So you've been describing how conditions work in C without knowing what
> the standard says about them.
> 
>> I don't think such expressions in C are much different from many other
>> languages, and I've implemented this too many times to be in need of
>> such guidance.
>>
>> The text talks about comparing the expression with 0, which is fine for
>> a programmer, but an implementer (this one, anyway) prefers it pinned
>> down a little more.
> 
> The description in the standard tells you everything you need to know to
> implement it, if you're willing to think about it a little.
> 
>> Since an equality comparison with 0 might need to take account of
>> multiple widths, and several types (int, pointer, float). A pseudo-bool
>> result is just one type, not even a width when there is no actual bool type.
> 
> A comparison with 0 may require a type conversion, as clearly described
> by the C standard.
> 
>> (Also, with certain languages I implement,
> [snip]
> 
> We were talking about C.  Of course if you're implementing something
> other than C, you should follow the rules of that language.

There are several approaches to describing what is happening. The 
language reference necessary has to choose one. That doesn't mean it is 
the only possible one. (Think about that when next quoting chapter and 
verse.)

And if you take it literally, it means that:

   if (a==b && c==d)

needs to treated as though it was written as:

   if ((a==b && c==d) != 0)

Although this will work, it is also unnecessary. With my approach, the 
if-expression must be 0 or 1, and the result of && is already 0 or 1.

Thread

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

csiph-web