🚀 go-pugleaf

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