Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!microsoft!jimad
From: jimad@microsoft.UUCP (Jim ADCOCK)
Newsgroups: comp.object
Subject: Re: C++ and garbage collection
Message-ID: <57716@microsoft.UUCP>
Date: 25 Sep 90 18:15:21 GMT
References: <2030@aber-cs.UUCP> <PCG.90Sep24181007@odin.cs.aber.ac.uk>
Reply-To: jimad@microsoft.UUCP (Jim ADCOCK)
Organization: Microsoft Corp., Redmond WA
Lines: 17

In article <PCG.90Sep24181007@odin.cs.aber.ac.uk> pcg@cs.aber.ac.uk (Piercarlo Grandi) writes:
|"Just to be clearer": _if_ Jim Adcock was referring to that class of
|machines and operating systems where each memory location has 4096
|(2^(32-20)) equivalent addresses, one can conventionally use one of
|these synonyms to indicate a heap pointer. So for example non-heap
|pointers may systematically use the 0th synonym, and heap pointers would
|use the 2048th. Hints of tagging...

Nah, because such address synonyms only apply to one obsolescent member of
the family.  Making use of such address puns is the moral equivalent of
people who play with the high bits in a 32 bit linear pointer -- because they
"know" their particular CPU board only implements 24 address lines. In any case,
making explicit use of address synonyms doesn't make much progress on 
the underlying problem, which is that segment and offset parts of a 
pointer are commonly stored separately, such that a "conservative" approach
requires the consideration of n^2 segment:offset word-pairs as "possible 
addresses of objects to be kept alive."