Date:	Sat, 8 Oct 1994 09:39:49 -0400 (EDT)
From:	Kimberley Burchett <OKRA AT max DOT tiac DOT net>
Subject:	Re: 16/32 (was: djgpp and the 386SX)
To:	DJGPP Mailing List <djgpp AT sun DOT soe DOT clarkson DOT edu>

On Fri, 7 Oct 1994, Frederick W. Reimer wrote:

> On Thu, 6 Oct 1994 terra AT diku DOT dk wrote:
> 
> > There is no execution time difference between 16-bit operations and
> > 32-bit operations for i[34]86.
> 
> I'll have to assume that you also have the 386+ programmer's reference 
> manual from Intel -- or at least have the instruction timings from some 
> (supposedly) 32-bit compiler?  Thanks for setting the facts striaght!

  Well, I do have a reference (HelpPC to be exact) and it says that there 
is a difference 'tween 16 and 32 bits when it comes to multiplication.  
For 16 bit MULs, the timing is 13-26 cycles.  32 bit MULs are 13-42 
cycles.  The actual time depends (I'm pretty sure) on how many bits are 
set in the numbers you're multiplying.
  So, the conclusion is that 32 bits CAN be slower, but only if you're 
multiplying something that really needs 32bits to be represented.  The 
thing is, if you tried to do the same multiplication using more than one 
16 bit MUL, it would take longer.  Depending on how you look at it, 32 
bits is faster AND slower. :)
							Kim

- Raw text -