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From: ahodgson@athena.mit.edu (Antony Hodgson)
Newsgroups: rec.games.programmer,comp.os.msdos.programmer,comp.graphics
Subject: Re: Need hard core help doing some 3d optimizations
Message-ID: <1991Apr12.142449.26807@athena.mit.edu>
Date: 12 Apr 91 14:24:49 GMT
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In article <1991Apr11.202429.29648@kuhub.cc.ukans.edu> 2fmlcalls@kuhub.cc.ukans.edu writes:
>> I just ran Turbo Profiler on some code of mine, and it looks like roughly
>> 90% of my CPU time is being shoved into one function.  Any help on the
>> optimizations would be really appreciated.
>
>I don't fully follow C, but I know float.  Go with scaled integers or longs and
>use integer division.  

Check out the latest Dr. Dobb's Journal.  In an article on memory mapped
numeric coprocessors, they claim that floating point division is now faster
than 386 integer division with the appropriate math coprocessor attached.

>As well, use scaled integers for your sin/co look=up
>tables (i.e. sin(45 degrees) = 707 rather than 0.707).  When you are through
>multiplying, do a div 1000 (or C equivalent of integer division).

If you go this route, consider scaling by a power of 2 rather than a power of
10.  You may be able to carry out divisions by shift operations rather than
division operations.

Tony Hodgson
ahodgson@hstbme.mit.edu