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Re: bart again (UCX64)

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From Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups comp.lang.c
Subject Re: bart again (UCX64)
Date Tue, 19 Sep 2023 05:53:46 -0700
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Ben Bacarisse <ben.usenet@bsb.me.uk> writes:

> Bart <bc@freeuk.com> writes:
>
>> On 12/09/2023 16:17, Ben Bacarisse wrote:
>>
>>> Malcolm McLean <malcolm.arthur.mclean@gmail.com> writes:
>>>
>>>> No we can't use Haskell.
>>>
>>> That's a shame.  The Glasgow Haskell compiler reports that in
>>>    sign ::  Double -> Int
>>>    sign x | x <  0 = -1
>>>           | x == 0 =  0
>>>           | x >  0 =  1
>>> the guards are non-exhaustive.
>>
>> You can do a much simpler check in any language that doesn't need
>> clever analysis or knowledge of the special properties of NaNs.
>>
>> Because the last return/last value is conditional, it can fail, but
>> there is no value associated with that failing path.
>
> But that is not always true.  Multiple conditions can be exhaustive.
> For example, Malcolm's sign:
>
>   double sign(double x)
>   {
>         if ( x <  0 ) return -1;
>         if ( x == 0 ) return  0;
>         if ( x >  0 ) return  1;
>         if (isnan(x)) return  x;
>   }
>
>> That can [be] provided in various ways including an 'else' branch
>> of an if-else-if chain.
>
> I think you are suggesting that [an explicit] "catch-all" should be
> given to make the compiler's job easier.  It maybe desirable from
> the point of view of controlling diagnostics but the result is less
> clear so I think it calls for a comment or even an assertion:
>
>   double sign(double x)
>   {
>         if (x <  0) return -1;
>         if (x == 0) return  0;
>         if (x >  0) return  1;
>         assert(isnan(x)); // all that's left...
>         return  x;
>   }

I agree with your sentiment about not worrying about making the
compiler's job easier.  For the code, though, I think it's better
to preserve the symmetry of the case tests, and put in a final
failure call - not to make the compiler's job easier, but to make
the intent more apparent to a human reader.  An assert() in place
of the final line would do the job instead, except that assert()
calls might be disabled by setting the macro NDEBUG.

  double sign(double x)
  {
        if (isnan(x)) return  x;
        if (x <  0  ) return -1;
        if (x == 0  ) return  0;
        if (x >  0  ) return  1;
        print_error_message_and_quit( "..whatever.." );
  }

Incidentally, putting the test for isnan(x) first allows the
function to work with signaling NaNs as well as quiet NaNs.
(I confess that I don't know if comparing a signaling NaN
to zero gives rise to a program exception.)

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Re: bart again (UCX64) candycane@f172.n1.z21.fsxnet (candycane) - 2023-09-06 19:53 +1300
  Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-07 12:00 -0700
    Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 16:33 -0700
      Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-07 20:55 -0700
        Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-07 22:16 -0700
          Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-08 07:09 +0000
            Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 10:10 +0200
              Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 01:30 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 11:26 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-08 10:44 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 13:26 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 01:57 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-09 18:36 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 18:19 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 13:28 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-10 13:20 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 15:19 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-10 16:07 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 18:33 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-10 15:44 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 18:36 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 01:48 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-09 19:04 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 02:47 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 16:03 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 16:06 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-09 01:52 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-08 18:16 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-09 21:31 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 12:03 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-10 21:36 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 08:51 +0200
                Re: bart again (UCX64) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-09-10 23:59 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 01:01 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 11:17 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 03:16 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 14:58 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 06:35 -0700
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-11 14:13 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 16:24 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 14:55 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 16:42 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-11 14:29 +0000
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 11:25 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 03:59 -0700
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-11 13:57 +0000
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 09:52 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 16:07 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-11 16:26 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 16:47 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-11 19:14 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-11 22:30 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 23:07 +0100
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-11 23:31 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 09:18 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 03:01 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 10:08 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-11 23:18 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-11 23:37 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 15:46 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-11 23:40 +0000
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 01:50 +0100
                Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-11 17:59 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-12 01:03 +0000
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 02:39 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 11:28 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 14:49 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 15:18 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 03:58 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-12 02:25 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 16:17 +0100
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 17:28 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 21:07 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 03:01 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 09:38 +0200
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 10:00 +0200
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-19 05:22 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-19 14:29 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 13:35 +0100
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 20:48 +0100
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-19 05:53 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-12 09:33 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-12 16:48 +0000
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-12 10:57 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-12 18:07 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 21:23 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 02:07 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 12:43 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 04:04 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 14:07 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 01:47 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 13:02 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 04:45 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 14:36 +0200
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-13 13:43 +0000
                Re: bart again (UCX64) James Kuyper <jameskuyper@alumni.caltech.edu> - 2023-09-13 11:10 -0400
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-13 17:12 +0000
                [meta] spam in thread Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 11:22 -0700
                Re: [meta] spam in thread Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-13 18:40 +0000
                Re: [meta] spam in thread Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 11:48 -0700
                Re: [meta] spam in thread David Brown <david.brown@hesbynett.no> - 2023-09-13 21:01 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 19:58 +0100
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-18 12:36 -0700
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-18 13:40 -0700
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-09-20 19:43 -0700
                Re: bart again (UCX64) "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2023-09-20 20:14 -0700
                Re: bart again (UCX64) Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2023-09-20 22:10 -0700
                Re: bart again (UCX64) Tim Rentsch <tr.17687@z991.linuxsc.com> - 2023-10-01 11:03 -0700
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 07:39 -0700
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-13 15:18 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 18:39 +0200
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 15:44 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-13 08:42 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-13 22:35 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-13 18:49 +0200
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-11 15:40 -0700
                Re: bart again (UCX64) Ben Bacarisse <ben.usenet@bsb.me.uk> - 2023-09-12 03:36 +0100
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 12:58 +0200
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 12:49 +0200
                Re: bart again (UCX64) Bart <bc@freeuk.com> - 2023-09-12 12:52 +0100
                Re: bart again (UCX64) Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2023-09-12 05:22 -0700
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-12 15:05 +0200
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 02:17 +0000
                Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-10 14:44 +0200
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-08 14:36 +0000
                Re: bart again (UCX64) Kaz Kylheku <864-117-4973@kylheku.com> - 2023-09-09 01:50 +0000
                Re: bart again (UCX64) scott@slp53.sl.home (Scott Lurndal) - 2023-09-09 15:40 +0000
          Re: bart again (UCX64) David Brown <david.brown@hesbynett.no> - 2023-09-08 09:57 +0200
          Re: bart again (UCX64) Richard Damon <Richard@Damon-Family.org> - 2023-09-09 10:23 -0700

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