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From: dricejb@drilex.UUCP (Craig Jackson drilex1)
Newsgroups: comp.arch
Subject: Re: 64 bits--why stop there?
Message-ID: <15428@drilex.UUCP>
Date: 9 Sep 90 03:35:53 GMT
References: <6106@vanuata.cs.glasgow.ac.uk> <2437@crdos1.crd.ge.COM> <1990Aug31.174957.9612@cimage.com> <3656@goanna.cs.rmit.oz.au> <1990Sep2.220249.19420@cimage.com> <5063@daffy.cs.wisc.edu>
Organization: DRI/McGraw-Hill, Lexington, MA
Lines: 33

In article <5063@daffy.cs.wisc.edu> bmiller@rt2.cs.wisc.edu (Brian Miller) writes:
>    Just off hand, would any of you familiar with past
>Burroughs machines care to provide some info on how they
>dealt with bit-oriented data?

Assuming that you're referring to the old Burroughs Large Systems (B6700, et
al), the basic bit-diddling operations were bit-field-extract and bit-field-
insert.  These only operated at a word level.  That is, you couldn't deal
with more than 48 bits at a time.

Examples:
A.[47:8]   Refers to the high-order byte of A.
A.[47:11]  Refers to the high-order 11 bits of A
A.[7:8]    Refers to the low-order byte of A.
A.[7:11]   Refers to the 8 low-order bits of A, plus the 3 high-order bits.

All of these causes extraction as an Rvalue, or insertion as an Lvalue.

A.[7:48]   Refers to the contents of A, end-around shifted 8 bits to the right,
	   (or 40 bits to the left)

This is most meaningful as an Rvalue.

There also was a combined operation called 'concat', which extracted
a field from one word and inserted it into a different place in a second
word.

Note that although I have used the past tense, all of this architecture
is still sold as the Unisys A-Series.
-- 
Craig Jackson
dricejb@drilex.dri.mgh.com
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