Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!apollo!gaz
From: gaz@apollo.COM (Gary Zaidenweber)
Newsgroups: comp.sys.atari.st
Subject: Re: Questions about ST Video Ram
Message-ID: <3e308bc4.52e@apollo.COM>
Date: 31 Aug 88 15:49:00 GMT
References: <657@uhnix2.uh.edu>
Organization: Apollo Computer, Chelmsford, Mass.
Lines: 25

From article <657@uhnix2.uh.edu>, by uace0@uhnix2.uh.edu (Michael B. Vederman):
> 
> Dear John,
(I love "dear John" letters :-) )
> 
> There is really one little problem with the code you have written, that being if
> the block you Malloc is just one byte past a 256 byte boundary, then you will
> be wasting 255 bytes, therefore you will need to Malloc at least (32K+255) to
> insure that you have at least enough memory to draw a full screen in.  Other-
> wise you will be overwriting memory which is not yours (a discussion of which
> 
> there has been an abundance of these days :-).
> 
> - Mike

Actually, the screen memory takes up 32000, not 32768 bytes (I got that from
a previous discussion.) Therefore, if you can malloc() 32K (32768) bytes, and
waste N bytes at the beginning, you have 768-N bytes of "padding" at the end
before you have to worry about touching memory which you don't own. Easy to
make this mistake (lucky motorola didn't call the processor the M69632, huh?)
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