Path: utzoo!utgpu!news-server.csri.toronto.edu!mailrus!wuarchive!zaphod.mps.ohio-state.edu!rpi!leah!bingvaxu!kym
From: kym@bingvaxu.cc.binghamton.edu (R. Kym Horsell)
Newsgroups: comp.lang.prolog
Subject: Re: Arrays in Prolog
Message-ID: <3997@bingvaxu.cc.binghamton.edu>
Date: 13 Sep 90 14:51:56 GMT
References: <90239.175243SCHMIED@DB0TUI11.BITNET> <1990Sep11.150245.26833@sics.se> <1990Sep12.170553.14414@cl.cam.ac.uk> <3996@bingvaxu.cc.binghamton.edu> <1990Sep13.071715.4852@sics.se>
Reply-To: kym@bingvaxu.cc.binghamton.edu.cc.binghamton.edu (R. Kym Horsell)
Organization: SUNY Binghamton, NY
Lines: 18

In article <1990Sep13.071715.4852@sics.se> matsc@sics.se (Mats Carlsson) writes:
\\\
>In Kym's scheme you would have to watch out for the magic bit in every
>trail entry.  This means extra work even if there are no value trail
>entries at all.
\\\

Yes extra work is involved on every trail access. However, how much
backtracking occurs when compared to, say, dereferencing
and taking into account that the usual stuff for reducing trailed
info seems fairly reasonable?

As I said, this extra bit _can_ be anywhere that's convenient.
Apropos of machine alignment checks, it _could_ be the low-order bit
of an otherwise address word. Personally, I don't like this, but
this idea _has_ been used various places with apparent success.

-Kym Horsell