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Re: Application Exercises

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Tim Rentsch <tr.17687@z991.linuxsc.com> writes:

> Richard Damon <Richard@Damon-Family.org> writes:
>
>> On 4/9/19 7:35 AM, Tim Rentsch wrote:
>>
>>> Challenge problem:  write a signed-integer equality determiner
>>> without using any comparisons:  no comparison operators, no
>>> conversions to bool, no &&, ||, or ?:, no if()'s, for()'s,
>>> or while()'s, and (the sneaky one) no switch()'s.  A nice
>>> little problem.  The gold standard is a solution that works
>>> on any conforming implementation.
>>
>> Presumably, +0 should be equal to -0?  (of course, this only applies if
>> you don't have a two's complement machine.
>
> Yes, that is my operating assumption:  the result should be the
> same as 'a == b', which AFAIK gives +0 == -0.

I didn't find it in the C standard in a quick search, but at least in
the case of the CDC 6000 series of computers -0 != +0, but the only way
to generate a -0 was to explicitly create it.  Any sequence of
arithmetic operations resulting in 0 resulted in +0.

>> I have a thought for a solution, but have the question if you are
>> allowed comparisons in pre-processor directives, so the only comparisons
>> are at compile time and not at execution time (with the assumption the
>> values are execution time values).  The issue is that I want to convert a
>> non-zero value to 1, which I can do without any comparisons, as long as
>> I know how many cycles of reduction to run, which needs preprocessor
>> comparisons, or hard wiring in knowledge of the number of bits in a
>> signed int.
>
> The code I wrote has one pre-processor comparison, to allow the
> code to work in different versions of C.  The test is this:
>
>     #if __STDC_VERSION__ > 199900
>
> The code does not assume any particular values or bounds for the
> number of bits in a signed int (or in intmax_t, which is the
> type used when compiling as C99 or later).

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Re: Application Exercises Richard Damon <Richard@Damon-Family.org> - 2019-04-06 14:23 -0400
  Re: Application Exercises Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-04-09 04:35 -0700
    Re: Application Exercises Ben Bacarisse <ben.usenet@bsb.me.uk> - 2019-04-09 13:29 +0100
      Re: Application Exercises Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-04-09 08:02 -0700
    Re: Application Exercises Richard Damon <Richard@Damon-Family.org> - 2019-04-09 22:15 -0400
      Re: Application Exercises Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-04-09 20:55 -0700
        Re: Application Exercises Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2019-04-09 22:21 -0600
          Re: Application Exercises Richard Damon <Richard@Damon-Family.org> - 2019-04-10 06:31 -0400
          Re: Application Exercises James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-04-10 07:43 -0400
        Re: Application Exercises Richard Damon <Richard@Damon-Family.org> - 2019-04-10 06:40 -0400
          Re: Application Exercises Tim Rentsch <tr.17687@z991.linuxsc.com> - 2019-04-10 08:15 -0700
      Re: Application Exercises James Kuyper <jameskuyper@alumni.caltech.edu> - 2019-04-10 07:37 -0400

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