Path: utzoo!utstat!news-server.csri.toronto.edu!cs.utexas.edu!samsung!xylogics!bu.edu!mirror!rayssd!galaxia!dave
From: dave@galaxia.Newport.RI.US (News Administrator)
Newsgroups: news.software.b
Subject: Re: Cnews artnum in active file
Message-ID: <995@galaxia.Newport.RI.US>
Date: 20 Aug 90 02:50:56 GMT
References: <1990Aug16.185023.26200@squirrel.mh.nl> <1990Aug17.034849.17801@zoo.toronto.edu> <1990Aug17.071243.16518@looking.on.ca>
Organization: Dave's Very Own Personal System
Lines: 39

In article <1990Aug17.071243.16518@looking.on.ca> brad@looking.on.ca (Brad Templeton) writes:
>In article <1990Aug17.034849.17801@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes:
>>of some stupid reader software.  (The lower number is basically an
>>inadequate kludge that smarter software should never look at, but there
>>is a lot of dumb software in the world, sigh...)
>
>Programs do need the minimum -- for creating reasonable sized bitmaps, for
>example.

Why do you assume that you can create a reasonable sized bitmap based on
the min and max article numbers?  If I have a high volume group that
happens to contain a few articles with long expiration dates I can still
get what would look like a huge group based on max-min but in fact it might
currrently contain significantly less than that.  At one point back in the
days of 2.10.1 (i.e. before the min field was introduced), I was concerned
about overflowing the bitmap array so I wrote a set of functions that
replaced all of the bitmap related macros and used a dynamically created
linked list as the data structure instead of using a statically created
array.  Obviously, calling a function and doing a linked list lookup is not
as fast as having a macro that does a few shifts and an array lookup, but I
challenge anybody to tell the difference between the two when they are
reading news with vnews/rn/trn/etc.  Maybe a really high performance
machine doing some kind of weird news processing in a tight loop could tell
the difference, but not a user who is generating a single bitmap access for
each article that gets displayed on their screen.  The linked list approach
has the really nice advantage of being very difficult to overflow.

I am still using the linked list approach in some programs I have that
analyze .newsrc files and they work quite nicely.  Since these programs are
not actually reading news articles, just analyzing .newsrc files, they are
primarily doing "bitmap" manipulations and I do not feel that they are
suffering any serious performance degradation from using the linked list
functions.

If anybody would like a copy of my code let me know and I will send it out.
-- 
David H. Brierley
Home: dave@galaxia.Newport.RI.US    Work: dhb@quahog.ssd.ray.com
Be excellent to each other.