Message-ID: <32BCFB1F.4FD6@gbrmpa.gov.au>
Date: Sun, 22 Dec 1996 17:10:55 +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
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To: Manuel Kessler <mlkessle AT wpax01 DOT physik DOT uni-wuerzburg DOT de>
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> <32B8ECAF DOT 5F9F AT gbrmpa DOT gov DOT au> <59bopp$vn3 AT winx03 DOT informatik DOT uni-wuerzburg DOT de>
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> :> 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.
 
> I have no manuals at my hands, but i KNOW that the pentium is capable of
> doing one fmul EVERY cycle, because i DID it. For serious problems you
> don't get that throughput, but something around 2 cycles per flop (fmul
> or fadd/fsub) is possible, if no memory is slowing things down. See the
> BLAS homepage at
>         http://cip.physik.uni-wuerzburg.de/~mlkessle/blas1.html
> For simple functions like dot product of short vectors coming out of the
> L1 cache it's possible to achieve 79 MFLOP at a P-133. This gives one
> fpu result every 1.6 cycles. Latency for both fmul and fadd is three cycles,
> therefore you have to use heavily fxch, but it's mostly free anyway.
> Of course, it's not very easy to get that performance, but it's
> possible.

And as Lord Shaman says:

> Anyway, even you are wrong, it's 3 clocks for the first mul, if the next
> FP operation is a mul, it goes through in 1 clock.

Which sounds about right... but then I thought this was in the lower
precision
modes. Maybe I should go check that... :)

Leathal.