Re: LZ: New idea for compression program!


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Re: LZ: New idea for compression program!



At 08:07 AM 9/11/96 -0500, you wrote:
>If the string contains the code to run the decompression
>program it will also have to contain the code to decide
>first if the decompression program is there or not, and
>if so, where.  Assuming the decompression program needs
>some memory to run in, the calling program will also need
>to decide if there is enough memory and refuse to call the
>decompression program if there isn't.


I see what you mean now.  Unfortunately, I don't really want
a shell.  It may be the only way, though.


>If it were me, I would keep it real simple.  I would have
>zshell run the decompression program which would make an
>uncompressed copy of the string and execute it.  Then,
>when the copy is finished it will do a ret and return to
>the decompressor, which will do a ret and return to zshell.


Exactly, but that is with a shell.  That is what I tried to
get away from.  I personally don't know much about the graphics
in ZShell.  I can, though, write software for the PC which will
compress the string and write a small program which is actually
added on to the comrpessed string.  Yah, yah, I told you this
already, I know.


I just think that it would be easier and better to see all of
the compressed programs just as if they were normal zshell
programs and then unzip them on the fly.  Why make a shell just
like zshell if I don't need to.


>I'd also try real hard to avoid having either zshell or
>the target program know anything about the compression,
>even if that means giving up some features.  Flexibility
>is much more important.


Why would they have to know about it?  ZShell will think they
are normal programs, the target program won't know either because
it will come out looking just like the original program stored on
the computer.


>There's been some discussion of changing PROGRAM_ADDR in
>zshell.  I would only do that after discussing it with the
>zshell people, and only with their approval.  Also, I would
>find out if it has to be restored before exiting.


I don't really see why.  Won't PROGRAM_ADDR automatically be set
if and when the decomrpession program and target program are run?
If I do a return from the decompression prgoram (after creating
the temporary string) and then have the compressed string run the
temp program, won't that work?


>Also, what other features of zshell might have to be dealt
>with.  Is PROGRAM_ADDR the only one?
>
>Memory is going to be needed to decompress the program into.
>I have no idea how that memory is obtained in zshell.  Does
>it have memory allocation routines or do you have all the
>rest of the calcs memory or is there no real control?  I
>haven't seen any discussion of this yet.  The memory needs
>to be there and your program has to know it's there and know
>how much, if possible.


That is what I am worried about (and this will be a problem
no matter how we do the decompression program).  How can you
create the variables and delete them?  Yes, the program needs
to know exactly how much, and whether it is enough.


>Barry
>
>
>


--	Scott Rein
	srein@rain.org


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