From: noring@netcom.com (Jon Noring)
Subject: A Bug in Fractint v17.2?  (Resurrecting an Oldie)
Organization: Netcom - Online Communication Services  (408 241-9760 guest) 
Date: Fri, 20 Nov 1992 16:52:16 GMT

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Hello,

Barry Smith sent me the following e-mail, and since he cannot post to the
net at this time, I decided to do it for him.  I'm sure he won't mind -
I did let him know I'll post it, and there's nothing personal in this
e-mail.

Jon Noring

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Date: Fri, 20 Nov 92 18:16:46 EST
From: bws555@cscgpo.anu.edu.au (Barry W Smith)
To: bws555@cscgpo.anu.edu.au, noring@netcom.com, twegner@mwunix.mitre.org
Subject: Data-dependent bug in Fractint?

In the now defunct newsgroup alt.fractals, quite a time ago (3 Mar 91) 
noring@netcom.COM (Jon Noring) said in an article with the subject: 'A 
bug in Fractint 15.1?':

                                  ***

In article twb@cbnewsh.cb.att.com (thomas.w.beattie) writes:

>I posted a Complex Newton fractal to the .pictures subgroup.
>For those of you who don't have access to that group (or prefer not to
>read it :-) here are the parameters and the fractint command line
>I used to generate it.
>
>Parameters:   12, 2, 12, 2
>Iter. limit:  2500
>Corners:      X[-6, 5]  Y[-4, 5]
>
>fractint type=complexnewton corners=-6/5/5/-4 params=12/2/12/2 maxiter=2500 per
iodicity=0
>
>This took 39 minutes on my 386/25 at 640x400x256c.

I used these parameters in Fractint 15.1 to generate this fractal using
1024x768x256 resolution.  When I was in the middle of the fourth scan
(after about 16 hours of computation), the program hit a math overflow
condition which bombed FRACTINT and put me back into DOS.  Suffice it to
say I was ticked!

Is there some bug in Fractint 15.1 that led to this abnormal termination?

Jon Noring

(BTW, I have a 386-33 without a coprocessor.)


[20-Nov-92 Update:  Haven't retried this yet.  I now have v17.2 and
a coprocessor, so when I get home, I'll fire up ol' Betsy.    Jon]


                                  ***

I had saved the capture log of this at the time, discovered it again 
during some recent electronic archaeology, and was moved to try this 
fractal out myself, using Fractint 17.2 and not 15.1, on a 386-25 
without a coprocessor.  Initially I used Super VGA 1024 x 768 x 16 
colours over two or three nights producing what seemed a very fine 
image.  However, after a bit over 18 hours in pass 4 of 4, Fractint 
crashed in a decidedly odd way.

When I tried to save the image with 
, or press other keys including 
<tab>, rectangular shaped splodges appeared about 30% down the screen 
and about 16 rows wide.  Each time I pressed 
, <tab>, <esc> or any 
other key, more splodges appeared.  These filled the left hand side 60% 
or so of the screen.  After I repeatedly hit keys, including <CR>, 
instead of splodges a series of vertical bars like a spectrum appeared.  
Nothing less than <Ctl>-<Alt>-<Del> would clear the screen or get me out 
of Fractint, but there was no math overflow or other DOS message.

I thought that I'd repeat the exercise with the same fractal, but a 
different resolution, and so tried again with black and white VGA (640 x 
480 x 2).   After 5 hours 48 minutes and while working on row 16 of pass 
3 of 3, the same thing happened.

So we have a fractal that bombs in three different resolutions and in 
two different versions of Fractint.

Is this a data-dependent bug?  How did Thomas W. Beattie create it?  It 
seems quite grotesque!

I would have posted this message as an article to the newsgroup, but my 
old VMS host has been shut down and this Unix beast (or perhaps its 
newsreader) and its editors do not like my PC or any of the terminal 
programs that I use to dial it up with, and the Unix support staff 
responded to my cries for help by saying (a) 'I never use a PC', and (b) 
'I don't use nn'.  :-( !!  One of these days I'll re-read the man pages 
and do some more experimenting, but meanwhile I can barely use news, 
while mail is fine.

Any comments?
--
Barry W Smith            P O Box 442, Jamison Centre ACT 2614, Australia
                                                     Tel. +61 6 251 2119
     Pegasus:            bsmith
     APC Networks:       peg:bsmith
     AARNet:             bsmith@peg.pegasus.oz.au
     Internet:           bsmith@peg.apc.org
     Internet/AARNet:    bws555@huxley.anu.edu.au
     Fidonet             Barry Smith 3:620/243@fidonet.org (PCUG Inc BBS)

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