Message-ID: <32B8ECAF.5F9F@gbrmpa.gov.au>
Date: Thu, 19 Dec 1996 15:20:27 +0800
From: Leath Muller <leathm AT gbrmpa DOT gov DOT au>
Reply-To: leathm AT gbrmpa DOT gov DOT au
Organization: Great Barrier Reef Marine Park Authority
MIME-Version: 1.0
To: shaman AT nlc DOT net DOT au
CC: djgpp AT delorie DOT com
Subject: Re: Is DJGPP that efficient?
References: <199612161347 DOT IAA01261 AT delorie DOT com> <32B8749B DOT 6DFD AT nlc DOT net DOT au>
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit

> I've got the original docs from the intel homepage for assembler
> programmers, and the Pentium floating point mul is nowhere near 3
> clocks. The throughput is something like 20 to 60 clocks depending on
> precision. The fastest version is about 4-6 clocks faster than the
> integer mul. On the other hand, the mmx can do 8 8 bit muls in a couple
> of clocks, and the Pentium Pro can do a 32bit mul in something like 3 or
> 4. Fixed point seems better by the moment. (I'd still use floating point
> for trig though)

Well, I have the Pentium Programmers Manual sitting in front of me in
Acrobat, and it says it _does_ do 3 cycles per mul. If you want proof
of the speed, look at Quake. Even Abrash said he couldn't get the same
performance out of the pentium with fixed point as he could with
floating point.

As for MMX, its just a heap of lookup tables on chip basically, and
isn't
all that good for serious work. High end stuff needs more precision
than 8 bit (ie: 64 bit) which is just one MMX register...no gain...
The MMX is cool for 8 bit or 16 bit games, but loses in high end
applications.

As for the Pentium Pro, dunno...I haven't read those manuals yet... :)

Leathal.