🚀 go-pugleaf

Clive D.W. Feather (clive@stdc.demon.co.uk) wrote:
: In article <46cu3i$6fg@solutions.solon.com>,
: Daniel Villeneuve <danielv@CRT.UMontreal.CA> wrote:
: > I know that the _result_ of comparing two pointers that do not belong to
: > the same array is undefined.

: No. The comparison is allowed to fail in some horrible way, not even
: returning a result. Certainly it doesn't have to return a *consistent*
: result.

And to give some rationale to this take segmented architectures. Here
the comparison operators only need to compare the offset in segment, not
the segment id [this is with the restriction that an object cannot be larger
than a segment.] This is more efficient as it saves having to do a comparison
of the segment id. The equality operators do need to check the segment id as
well.

For example if 'a' is 101:25 and 'b' is 120:25  ( <segment-id>:<offset> )
then:
       a != b                   #segment if checked
       a <= b      
       a >= b      
       !( a = b )               #segment id checked
       !( a > b  )
       !( a < b  )

which is not much use as an ordering.

It is a bit annoying that there is no full ordering on pointers as are a 
number of occasions it would be useful.

--
Stephen Baynes                              baynes@mulsoc2.serigate.philips.nl
Philips Semiconductors Ltd
Southampton                                 My views are my own.
United Kingdom