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From: muts@fysaj.fys.ruu.nl (Peter Mutsaers /100000)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Floating Pt. Math with a 68881 not always faster
Message-ID: <1435@ruunsa.fys.ruu.nl>
Date: 3 Sep 90 11:58:04 GMT
References: <8379@ncar.ucar.edu>
Sender: news@ruunsa.fys.ruu.nl
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moses@hao.ucar.edu (Julie Moses) writes:

>Q- Can someone explain why?

>     My best guess is that the time the processor takes to transfer
>the floating point numbers and also the time waiting for the math
>copressor to be ready to receive makes the simpler math operations
>slower than just doing them inside the 68000 chip. I am using the
>Prospero math libraries that look once for the math chip so that one
>must link for either a 68K chip with or without the math chip, 
>exclusively.

>Julie Moses

Maybe the routines of Prospero are not very fast, or they are only
single precision.

The 68881 uses 80 bits, generally double precision takes 4 times longer
then single precision.
In Turbo C, which has the fastest floating point library available to my
knowledge, 80 bits take 3 times as long as the 68881 does. So
if there were single pricision routines they would be a bit faster
then the 68881.
--
Peter Mutsaers                          email:    muts@fysaj.fys.ruu.nl     
Rijksuniversiteit Utrecht                         nmutsaer@ruunsa.fys.ruu.nl
Princetonplein 5                          tel:    (+31)-(0)30-533880
3584 CG Utrecht, Netherlands