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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.programming
Subject: Re: A little puzzle.
Date: Tue, 29 Nov 2022 04:03:46 -0800
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Richard Harnden <richard.nospam@gmail.com> writes:

> On 28/11/2022 15:30, Tim Rentsch wrote:
>
>> Richard Harnden <richard.nospam@gmail.com> writes:
>>
>>> On 21/11/2022 20:45, Ben Bacarisse wrote:
>>>
>>>> I wonder if there are any real posters here?  Let's see...
>>>>
>>>> I came across a trivial programming task that must have been
>>>> solved a thousand times by other programmers, but it had never
>>>> crossed my path until yesterday.  I must be feeling my age
>>>> because I made a real hash of tackling it at first.  Anyway, I
>>>> thought it might be of interest.
>>>>
>>>> Consider any ordered measure that "wraps round" -- bearings in
>>>> degrees, minutes in the hour, indeed hours in either the 12 or 24
>>>> hour clock.  The problem is to determine if a given value is in
>>>> the sub-range specified by a start and an en value.
>>>>
>>>> I was specifically concerned with integer values where the
>>>> sub-range includes the start value but excludes the end value.
>>>> [...]
>>>
>>> I think this works ...
>>>
>>> int in_subrange(int range, int start, int end, int check)
>>> {
>>>      check %= range;
>>>
>>>      if (  ( end < start && (
>>>                 (check >= 0 && check <= end)
>>>              || (check >= start && check < range)
>>>              )
>>>            )
>>>         || ( check >= start && check <= end )
>>>         )
>>>              return 1;
>>>
>>>      return 0;
>>> }
>>
>> Have you thought about a case where the values of check, start,
>> and end are chosen from the interval -9000000000 to 9000000000?
>> How about the interval -18000000000 to 18000000000?
>
> Nope, I assume that start and end are between zero and range, and
> that check is greater that zero.

This assumption doesn't match the problem statement (emphasis
added):

    Consider >> any << ordered measure that "wraps round"

What's being asked for is a function that will work with any
ordered measure (that wraps), not just some such measures.  An
example of such a measure is longitude, which goes from -180
to +180 (with one of the two extreme values omitted).  Similarly
there is no reason not to allow a measure that is only positive
integers but does not include zero.  An important part of the
challenge is to come up with a solution that handles these cases
as well as the more obvious ones.