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From: tp@ndm20
Newsgroups: net.arch
Subject: Re: ORed indexes
Message-ID: <34500002@ndm20>
Date: Sun, 11-May-86 10:06:00 EDT
Article-I.D.: ndm20.34500002
Posted: Sun May 11 10:06:00 1986
Date-Received: Tue, 13-May-86 08:45:14 EDT
References: <5100066@ccvaxa>
Lines: 23
Nf-ID: #R:ccvaxa:5100066:ndm20:34500002:000:1021
Nf-From: ndm20!tp    May 11 09:06:00 1986


>digress.)  If you set more than one of the three bits in the index register
>field, the corresponding registers were or'ed together before they were
>subtracted from the base address.  Sounds handy, no?  Well, no.  It was

>that almost every 7090 program worked on the 7094, which means that nobody
>used the or'ing.  Pfui.

The  Harris  H-series  (24  bit  architecture, proprietary  OS) has a
similar wierdness.  SOME instructions allow exactly what is described
above,  but not  in indexing,  these are  direct register references.
These are machines that are around  today.   I doubt  anyone uses the
feature, since the assembler doesn't give you  a way  to set multiple
bits (not documented anyway).  In some cases it  would be  nice.  You
could  or  registers  on  a  move  operation, thus  saving several or
instructions.

Terry Poot
Nathan D. Maier Consulting Engineers
(214)739-4741
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