Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!uwvax!umn-d-ub!nic.MR.NET!srcsip!coltrane!carpent
From: carpent@coltrane.SRC.Honeywell.COM (Todd Carpenter)
Newsgroups: comp.sys.amiga
Subject: C help (Long) : Dynamic Allocation and Globals
Message-ID: <23129@srcsip.UUCP>
Date: 6 Jun 89 02:38:47 GMT
Sender: news@src.honeywell.COM
Lines: 60


Hello, oh great and mighty C wizards of the net!  I beg of thee guidance...
 
  Okay, these are not *pure* amiga questions.  But I am writing (what I think
  will a be useful and impressive) program on my amiga, and have encountered a
  few stumbling blocks.   Please *email* me replies.
 
  1) Speed is the prime consideration.  This will *not* be a small program by
  any means, but it has to be fast.

  2) But, it is also big.  The data arrays for small systems are over 256K.
  and I have multiple arrays.  SO I can't waste too much space.

Question 1)  People have been talking about residentable programs, and
generally good (for the Amiga) programming techniques.  One of the points is to
avoid global variables.  But I cannot think of any way to avoid global
variables, without suffering a hit in performance.
 
  unsigned moo(param1,param2,iteration)
     unsigned param1,param2
  {
     return( (param1 - param2 < 0) ||
               (iteration & MASK == MASK) )
  }

Now, moo is one of many functions which return true or false.  Which function
is chosen (and initialized) at the begining.  A pointer to moo is returned (so
I oont have to go through a SWITCH statement).   So I want a generic interface
to those functions, and the above interface *should* be sufficient.  However,
some of the routines require a few items (MASK in the above) initialized by the
user.  These values are set once, at the beginning, or may actually change
through events other than that within moo.  So, how do I get MASK to moo
without using globals?  I *don't* want to pass it in (since it would be a non
uniform interface), and I don't want to have a test to see if it is an
initialization phase.
 
  related - what about static variables inside moo?  Will they cause troubles?


Question 2:  This is another embarrassing one.  I can't afford to waste space,
so I'd like to declare my arrays to be only as large as necessary.  These
two dimensional arrays are indexed very frequenty.
  
    How do I allocated from the heap the following:

unsigned short MOO [Xdimension] [YDimension];

    Where X and Y are determined at runtime (256x256 would be considered
    reasonable values)?

    if I pass MOO to a procedure, how do I reference element MOO[x][y]?  Do I
    start building pointer offsets and other ickies, or are there nice ways?


Thanks in advance! 

Todd P. Carpenter          Honeywell Systems and Research Center
voice:  (612)782-7229      paper:  3660 Technology Drive, Minneapolis, MN 55418
UUCP: carpent@srcsip.uucp  bang-style: {umn-cs,ems,bthpyd}!srcsip!carpent
Internet: carpent@src.honeywell.com or carpent@altura.honeywell.com