Xref: utzoo rec.games.programmer:3433 comp.os.msdos.programmer:4707 comp.graphics:17299
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!uwm.edu!rutgers!news.cs.indiana.edu!maytag!watstat.waterloo.edu!dmurdoch
From: dmurdoch@watstat.waterloo.edu (Duncan Murdoch)
Newsgroups: rec.games.programmer,comp.os.msdos.programmer,comp.graphics
Subject: Re: Need hard core help doing some 3d optimizations
Message-ID: <1991Apr17.133142.24149@maytag.waterloo.edu>
Date: 17 Apr 91 13:31:42 GMT
References: <1991Apr11.202429.29648@kuhub.cc.ukans.edu> <1991Apr13.154112.11345@dircon.co.uk> <1991Apr16.210819.17873@cs.fau.edu>
Sender: news@maytag.waterloo.edu (News Owner)
Organization: University of Waterloo
Lines: 28

In article <1991Apr16.210819.17873@cs.fau.edu> conners@cs.fau.edu (Sean Conner) writes:
>
>  So, okay, I have a MIPS system.  No problem.  But what about us poor
>programmers who can only afford a 386/387 system?  It is still faster to
>use ints than floats, for two reasons:
>
>	1.  On a 386, the longest a IDIV will take (this is with a memory
>	    operand here) is 46 cycles.  And the longest an IMUL will take
>	    is 41 cycles.  On the 387, the SHORTEST time it will take to
>	    divide two reals is 91 cycles.  A floating point multiply takes
>	    about the same as the IMUL instruction (depends on addressing
>	    modes, though).  

Just in case you're interested:  the times for the 486 are

  IDIV    19-44
  FDIV    73
  IMUL    13-42
  FMUL    11-16

So it looks as though floating point math would be a contender, even without
a MIPS, as long as you avoided the divides.  I don't know the algorithms
you want to use, but very often the denominator in a series of divides stays the
same for a long time, so you can replace it with a series of 
multiplies by the reciprocal.

Duncan Murdoch
dmurdoch@watstat.waterloo.edu