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From: cet1@cl.cam.ac.uk (C.E. Thompson)
Newsgroups: comp.lang.postscript
Subject: Re: defeating save/restore
Keywords: images, data compression,
Message-ID: <1991Mar11.145130.12027@cl.cam.ac.uk>
Date: 11 Mar 91 14:51:30 GMT
References: <38972@netnews.upenn.edu> <1909@chinacat.Unicom.COM>
Reply-To: cet1@cl.cam.ac.uk (C.E. Thompson)
Organization: U of Cambridge Comp Lab, UK
Lines: 23

In article <1909@chinacat.Unicom.COM> woody@chinacat.Unicom.COM (Woody Baker @ Eagle Signal) writes:
>
>I seem to remember that on at least on older version of PS, there was a bug
>that allowed you to do this.  I think it was something like if you created
>a string, then put a character into it with put, it would survive a
>save/restore pair.  I know that Don Lancaster published some thing about it,
>and even wrote code to use it, but IT IS A BUG AND IS NOT REPEATABLE
>unless you have the buggy interpreter.
>
>i.e.  Not wise to write code for others use that depends on it.
>
Well, there are much cleaner ways of passing data out through a save/restore
boundary than to use this feature/bug. However, it is morally certain that 
all PostScript interpreters that have ever existed have had the feature/bug.
In fact, in the 2nd edition of the LRM (orange-and-white book) Adobe seem to
have given up claiming that this will ever change. Page 60, section 3.7.3,  
"restore resets the values of all composite objects in local VM, except  
strings, to their state at the time of the save"; and there is no equivalent
to the footnote on p.44 of the old LRM (red book). 

Chris Thompson
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