Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!concertina!fiddler
From: fiddler%concertina@Sun.COM (Steve Hix)
Newsgroups: comp.sys.mac
Subject: Re: Stats on 68881
Message-ID: <38058@sun.uucp>
Date: 6 Jan 88 20:50:42 GMT
References: <8368@steinmetz.steinmetz.UUCP>
Sender: news@sun.uucp
Lines: 26

In article <8368@steinmetz.steinmetz.UUCP>, (Jeff A. Hallett) writes:
> 
> Does anyone know how fast the 68881 can do a multiply-add?

Well, it depends...

What clock rate is your 68881 running at? 

What is the format of the memory source or destination
operand?  What addressing mode are you using? (If I'm
reading one of the tables in the "MC68881 Floating-
Point Coprocessor User's Manual" rightly, the FMUL
instruction can take anywhere from 71 to 908 cycles
to execute.  This don't allow for instruction/data
fetch and write time...

It might be easier to just find a Mac with the chip
in it and write your own benchmark to exercise the
'881 and find a typical time for the application sort
of thing you're doing.  (But we all know about bench-
marks, don't we? :} )

Or you could get the Motorola '881 manual (MC68881UM/AD)
and wallow around in Chapter 6 for a while.

	seh