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From: allen@gitpyr.gatech.EDU (P. Allen Jensen)
Newsgroups: comp.lang.c
Subject: Re: Query: Implementation with non-zero NULL
Message-ID: <3675@gitpyr.gatech.EDU>
Date: Mon, 1-Jun-87 14:54:56 EDT
Article-I.D.: gitpyr.3675
Posted: Mon Jun  1 14:54:56 1987
Date-Received: Wed, 3-Jun-87 01:49:23 EDT
References: <158@delftcc.UUCP> <3673@gitpyr.gatech.EDU>
Organization: Georgia Institute of Technology
Lines: 18
Keywords: C, NULL, portability
Summary: CORRECTION TO PREVIOUS REPLY

In article <3673@gitpyr.gatech.EDU>, allen@gitpyr.gatech.EDU (P. Allen Jensen) writes:
> are expected.  Because of this, constructs such as the
>        if(p)
> Do not yield correct results.  The prime also has modes of operation in which
> pointers are 48 bits even though long, int and float are all 32 bits.
> This is a hold-over from the segmented addressing of the older 16 bit primes.
> The value of NULL is 0x60000000 on a prime.
> 
> P. Allen Jensen

Correction - if(p) yields  false if p = (char *) NULL
Also, if(p != 0) also yields false.  The 0 is cast to (char *).

The value of 0x60000000 is correct.  If you do a union with a long and compare
the long with zero (0), they will not be equal.  Also, since in some modes
a pointer may be 48 bits, you would only get the first 32 bits in the union.

P. Allen Jensen