Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.unix.wizards
Subject: Re: brk's zero-fill behavior on VAXen (useful undefined checks)
Message-ID: <7315@utzoo.UUCP>
Date: Tue, 11-Nov-86 18:44:09 EST
Article-I.D.: utzoo.7315
Posted: Tue Nov 11 18:44:09 1986
Date-Received: Tue, 11-Nov-86 18:44:09 EST
References: <7208@elsie.UUCP> <5142@brl-smoke.ARPA> <2447@hcr.UUCP>, <363@yabbie.rmit.oz>
Organization: U of Toronto Zoology
Lines: 12

> ... When a new() is done, a unique key is tacked on top of the object
> allocated, that must match the key in the pointer referencing it, otherwise
> a "pointer-invalid" run-time error occurs.
> 
> On the cyber, this is easy, since there are so many bits available in a word.

Yet another similar trick:  in the Algol 68 implementation for the Cyber,
from CDC Netherlands I think it was, the garbage collector uses the extra
bits in the pointers as mark bits, thereby using zero extra storage!
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,decvax,pyramid}!utzoo!henry