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From: nelson_p@apollo.HP.COM (Peter Nelson)
Newsgroups: comp.lang.c++,comp.lang.c
Subject: Re: Zortech "limitation"
Message-ID: <4895d648.20b6d@apollo.HP.COM>
Date: 11 Feb 90 19:59:00 GMT
Sender: root@apollo.HP.COM
Distribution: usa
Organization: Hewlett-Packard Apollo Division - Chelmsford, MA
Lines: 53


                                       

   I received a number of responses to my query about how to
   allocate large, global 2-dimensional arrays in Zortech C++,
   where no individual array would be > 64K but the total
   space involved for all of them would exceed 64K.  One
   of my requirements is that I can access them as 2-dimensional
   arrays and not have to access them via pointer arithmetic.

   Most of them involved extensive use of malloc and pointers.

   The whole idea of using a high-level language in the first
   place is to make the architectural ideosyncracies of the 
   machine INVISIBLE to the user and allow the user to express
   the program in terms of his problem.  In my case that means
   2 dimensional arrays.   

   There is no **technical reason** why the Zortech compiler
   can't allow you to allocate arbitrarily large amounts of
   global memory, up to the limitations of available RAM, and
   simply manipulate the DS register to access it.  Sure, there's
   more overhead, but the manual already warns the user that the
   use of the C or L memory models is less efficient, so we
   must presume that the user is willing to pay that price.  

   On a virtual memory machine I know that if I allocate 
   an array that exceeds the size of my available physical 
   RAM I'm going to pay a huge performance penalty due to
   paging.   But if I'm willing to live with that then I 
   don't have to write my program any differently.    

   80x86 machines have their segmented architecture but virtually
   ALL computers have lots of addressing modes and different length
   address or offset registers, with different numbers of ticks
   required to execute them.  But our C compilers here at work don't
   ask me what addressing modes or register sizes to use.  Hell, 
   I don't have to even worry about rewriting my program when
   I go from, say, a 68030 platform to an Apollo DN10000 (RISC).
   If I *want* to tune the program I have large selection of 
   options, but I'm not forced to use them.  

   With the Zortech product, as well as some other DOS products,
   I apparently have to return to those "golden days of yesteryear"
   and be a hobbyist hacker again.  And I thought I'd paid those 
   dues and graduated to software adulthood already.

                                                ---Peter