From: eachus@spectre.mitre.org (Robert I. Eachus)
Subject: Re: null pointer representation (was: Boolean Representation)
Date: 1998/10/02
Date: 1998-10-02T00:00:00+00:00 [thread overview]
Message-ID: <EACHUS.98Oct2143045@spectre.mitre.org> (raw)
In-Reply-To: yec1zotnlor.fsf@king.cts.com
In article <yec1zotnlor.fsf@king.cts.com> Keith Thompson <kst@king.cts.com> writes:
> Even if there weren't any such machines, I don't believe that the
> assumption that System.Null_Address is all zero bits would be
> justified -- though admittedly my argument would be a bit weaker.
Some years back at Stratus, we used one not zero as the value for
null pointers, since it trapped if dereferenced. When the 68020 came
along, we temporarily switched to xFFFFFFFF (I don't think that
version ever shipped.) Then to a version of the OS where page zero
was inaccessable in user mode so that we could use zero as a null
address in user code.
--
Robert I. Eachus
with Standard_Disclaimer;
use Standard_Disclaimer;
function Message (Text: in Clever_Ideas) return Better_Ideas is...
next prev parent reply other threads:[~1998-10-02 0:00 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
1998-09-24 0:00 Boolean Representation matthew_snyder
1998-09-24 0:00 ` dewarr
1998-09-24 0:00 ` Samuel T. Harris
1998-09-25 0:00 ` dewarr
1998-09-27 0:00 ` Samuel T. Harris
1998-09-28 0:00 ` dewar
1998-09-24 0:00 ` matthew_snyder
1998-09-24 0:00 ` dennison
1998-09-24 0:00 ` Tom Moran
1998-09-25 0:00 ` dewarr
1998-09-25 0:00 ` Tom Moran
1998-09-25 0:00 ` dewarr
1998-09-25 0:00 ` Robert I. Eachus
1998-09-24 0:00 ` dennison
1998-09-24 0:00 ` Keith Thompson
1998-09-25 0:00 ` dennison
1998-09-25 0:00 ` Keith Thompson
1998-09-26 0:00 ` Tucker Taft
1998-09-26 0:00 ` Keith Thompson
1998-09-27 0:00 ` null pointer representation (was: Boolean Representation) Arthur Evans Jr
1998-09-27 0:00 ` Keith Thompson
1998-09-28 0:00 ` dewarr
1998-09-28 0:00 ` Lieven Marchand
1998-09-28 0:00 ` Keith Thompson
1998-09-28 0:00 ` dewarr
1998-09-30 0:00 ` Keith Thompson
1998-10-02 0:00 ` Robert I. Eachus [this message]
1998-09-27 0:00 ` Boolean Representation dewarr
1998-09-27 0:00 ` dewarr
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