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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.programming
Subject: Re: A little puzzle.
Date: Mon, 21 Nov 2022 17:39:44 -0800
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Ben Bacarisse <ben.usenet@bsb.me.uk> writes:

> 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.

The question I think you're asking is to write a function like this

    /* is_circularly_between( a, b, c ) -
     *     1 if b is circularly between a and c,
     *     0 otherwise
     *     interval [ a, c ) is closed at the 'a' end, open at the 'c' end
     *
     *     The parameters a, b, and c are all of a single type T,
     *     where T allows relational (ordering) comparisons.
     *
     *     Assumes a, b, and c all have legitimate values.
     */

    int
    is_circularly_between( T a, T b, T c ){
        /* to be determined */
    }

with T being some integer type.  Assuming this is right I have
written such a function (but am not posting it just yet).


> Though I am not sure this merits the term "puzzle", I suggest that
> solutions be posted with some spoiler protection.

That's good, thank you for the reminder.

> Do all the news
> readers used by programmers (or ex programmers) all respect the presence
> of a form-feed character...
> Next page...

Mine does, for some values of "respect".  It does have the property
that it hides what follows.