Path: utzoo!attcan!uunet!cs.utexas.edu!sdd.hp.com!apollo!rehrauer
From: rehrauer@apollo.HP.COM (Steve Rehrauer)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: Floating Pt. Math with a 68881 not always faster
Message-ID: <4c9b94c0.20b6d@apollo.HP.COM>
Date: 4 Sep 90 14:09:00 GMT
References: <8379@ncar.ucar.edu> <2271@atari.UUCP> <989@nikhefh.nikhef.nl>
Sender: root@apollo.HP.COM
Reply-To: rehrauer@apollo.HP.COM (Steve Rehrauer)
Organization: Hewlett-Packard Apollo Division - Chelmsford, MA
Lines: 18

In article <989@nikhefh.nikhef.nl> t68@nikhefh.nikhef.nl (Jos Vermaseren) writes:
>If you find that multiplication is faster without the chip you have
>either an incredibly fast FP library, or an inefficient link to the
>68881.

It's also worth noting that the 68882 can overlap execution of f.p.
instructions, assuming there aren't any operand dependencies.  The
68040 (which doesn't implement the full '881/'882 instruction set,
but does do the "core" -- FMUL, FDIV, etc) also overlaps, and (since
it directly implements the instructions itself) doesn't incur any
of the coprocessor overhead of a '881/'882.

In other words, there's good reasons to not do floating-point in
software, even if you can shave a few clocks in a few instances
on your current hardware by doing so.
--
   >>"Aaiiyeeee!  Death from above!"<<     | (Steve) rehrauer@apollo.hp.com
"Spontaneous human combustion - what luck!"| Apollo Computer (Hewlett-Packard)