Re: BETWEEN

"Jerry Avins" <jya@[EMAIL PROTECTED]
> wrote in message
news:rIadnSizg9q1YUjanZ2dnUVZ_gWdnZ2d@[EMAIL PROTECTED]
> Ed wrote:
> > WITHIN  was meant to replace  BETWEEN  but it hasn't always
> > been a comfortable fit.
>
> The other way around. WITHIN came first. It may be as nice, but its code
> is so snazzy that I find it more esthetically pleasing.

In the version I show, the algorithms are very similar.  WITHIN uses
U< whereas BETWEEN uses U<= .

AFAIK, BETWEEN can't be made from WITHIN and vice-versa so
it suggests they're equally primitive.  Both seem to have their
applications.

> > A characteristic of  WITHIN  is that the upper limit is not included
> > in the range.  This can lead to obfuscated code e.g.
> >
> >     CHAR a   CHAR z  1+   WITHIN
> >
> > Thus the functionality of  BETWEEN  is still being used, if not
> > the word itself.  When defined today, it is usually as:
> >
> > : BETWEEN ( n1|u1 n2|u2 n3|u3 -- flag )   1+ WITHIN ;
>
> Clearly, WITHIN came first in this case.

Only because Forth-94 systems are likely to have it :)

> > But it is not without problem  e.g. it fails when  u1 =  u3  =  MAX-U
.
>
> It is the comparison operator in the definition that "fails".
>
> > Perhaps not so significant for 32-bit systems as for 16-bit, it is
> > nevertheless an inconsistency which can catch a programmer
> > unawares.
>
>
> > Playing with the algorithm for WITHIN (A.6.2.2440) one gets:
> >
> > : BETWEEN  ( n1|u1 n2|u2 n3|u3 -- flag )   OVER - -ROT - U< 0= ;
>
> Check the limiting cases of U> .

I haven't noticed a problem as yet.  My experience/knowledge
of computer math is limited, hence the request.