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From: paulh@cimage.com (Paul Haas/1000000)
Newsgroups: comp.arch
Subject: Re: 64 bits--why stop there?
Message-ID: <1990Sep2.220249.19420@cimage.com>
Date: 2 Sep 90 22:02:49 GMT
References: <6106@vanuata.cs.glasgow.ac.uk> <2437@crdos1.crd.ge.COM> <1990Aug31.174957.9612@cimage.com> <3656@goanna.cs.rmit.oz.au>
Reply-To: paulh@dgsi.UUCP (Paul Haas/1000000)
Organization: Cimage Corp, Ann Arbor, MI
Lines: 44

In article <3656@goanna.cs.rmit.oz.au> ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe) writes:
>In article <1990Aug31.174957.9612@cimage.com>, paulh@cimage.com (Paul Haas/1000000) writes:
>> Adding bit pointers to C compilers would be easy on machines which
>> already have multiple incompatible pointer types.  Bit-pointers would
>> be just one more type.  On nicer machines, you have to teach the
>> compiler about multiple pointer types
>
>Not at all.  Nobody was proposing a new kind of pointer.  The suggestion
>was to have *one* kind of address *only*, namely a bit address.  Only the
>size of addressible units was to change.

Bit address pointers seem like a new kind of pointer to me (-:.
In C-speak the new type of pointer would be "pointer to bitfield",
"pointer to bit", or "pointer to short short char" (look ma, no new
keywords).

If bit-addressing is used, it can happen in several orders:
   1) Hardware and programmer interface at the same time.
         A computer vendor (MIPS, Sun, HP, IBM, DEC, etc...) decides that
         bit addressing is the wave of the future and designs it into their
         next generation architecture at considerable cost.  They enhance
         C, FORTRAN, Cobol and/or Ada, so the programmers can actually
         take advantage of the bit addressing.
   2) Hardware first.
         The computer vendor adds bit-addressing to the hardware, but
         doesn't provide an interface in their higher level languages.
         (Prime Computer used a variant of this in the seventies, where
         they didn't ever finish the hardware support, as Richard pointed out).
         The cost is still considerable, nothing is gained.
   3) Programmer interface first.
         Someone (compiler maintainer for a computer vendor, independent
         compiler writer, anyone with the source for GCC, etc...) decides
         that bit addressing is the wave of the future and adds a way
         to use bit addressing to an existing compiler on existing hardware.
         This does imply multiple pointer types.  The cost would be measured
         in person weeks.  (Could it be done in a header file in C++ ?)

Does anyone seriously believe that a sane computer vendor will create
a new flavor of hardware in the nineties, with no evidence of any
customers?
---
I'm not a C++ expert, but it seems to me, that it would be possible to
define bit pointers
to add a bit type and pointer to bit