Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!waikato.ac.nz!ldo
From: ldo@waikato.ac.nz (Lawrence D'Oliveiro, Waikato University)
Newsgroups: comp.arch
Subject: Re: Bitfield instructions--a good idea?
Message-ID: <1991Apr18.165322.3489@waikato.ac.nz>
Date: 18 Apr 91 16:53:22 +1200
References: <1991Apr17.174918.3458@waikato.ac.nz> <715@seqp4.UUCP>
Organization: University of Waikato, Hamilton, New Zealand
Lines: 27

In article <715@seqp4.UUCP>, jdarcy@seqp4.ORG (Jeff d'Arcy) writes:

> Unlike your name, mine has a small "d".  I'm sure you understand.

Whoops! After all the fuss I make about people spelling *my* name
correctly, please accept my humble apologues.

  [detailed example of emulating power-of-two operand scaling
   using just two bitfield instructions, ending with]
> Hence, the "inconvenience" of Motorola's encoding is actually a win.

I agree you haven't lost anything in this example, but I don't see
that you've gained anything, either, other than saving a register.
Your example works OK on this architecture, mine would work less
well, and that's all.

Todd Bridges (toddb@illini.sps.mot.com) has, if I understand him
correctly, given me what I think the real reason is for these
instructions being defined the way they are: 88K instructions can't
have more than three operands.

Lawrence D'Oliveiro                       fone: +64-71-562-889
Computer Services Dept                     fax: +64-71-384-066
University of Waikato            electric mail: ldo@waikato.ac.nz
Hamilton, New Zealand    37^ 47' 26" S, 175^ 19' 7" E, GMT+12:00
Whoever said "There is no such thing as a free lunch" obviously never
heard of the Buy-No-Meal Theorem.