Date: Wed, 8 Jan 1997 08:31:12 +0800 (GMT)
From: Orlando Andico <orly AT gibson DOT eee DOT upd DOT edu DOT ph>
To: djgpp AT delorie DOT com
Subject: Re: Fixed Point (Optimization)
In-Reply-To: <qwbRXBActG0yEwWC@foobar.co.uk>
Message-ID: <Pine.SGI.3.93.970108082917.19523G-100000@gibson.eee.upd.edu.ph>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII

On Mon, 6 Jan 1997, Paul Shirley wrote:

[...]
> First: floating point is slower at add and subtracts. If all you ever do
> is add/sub then integer will be 2* faster *at least*. If you use
> multiplies floating point is ~4-12* faster. Pipelined you get that 12*
> speedup.
> Divides are slightly faster in fpu but a lot less hassle than fixed
> point. If you use single precision fpu mode they are always 2* faster.
> Also its possible to continue issuing integer instructions while a float
> divide executes. That allows tricks like performing a perspective divide
> in effectively 1 clk.
[...]

is this true for 486's? or just Pentiums? i'm hacking at some MPEG audio
code (MAPLAY -- UNIX-based really) so that it can run faster on 486's (the
generic MAPLAY chokes on anything less than a Pentium-60) and I would love
to learn about quickie speedups of FP code.

thanks

.-----------------------------------------------------------------.
| Orlando Andico                email: orly AT gibson DOT eee DOT upd DOT edu DOT ph |
| IRC Lab/EE Dept/UP Diliman   http://gibson.eee.upd.edu.ph/~orly |
|  "through adventure we are not adventuresome" -- 10000 Maniacs  |
`-----------------------------------------------------------------'