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From: ggs@ulysses.UUCP (Griff Smith)
Newsgroups: comp.lang.c
Subject: Re: machines with oddball char * formats
Message-ID: <1475@ulysses.UUCP>
Date: Tue, 18-Nov-86 08:42:31 EST
Article-I.D.: ulysses.1475
Posted: Tue Nov 18 08:42:31 1986
Date-Received: Tue, 18-Nov-86 21:15:18 EST
References: <1011@zog.cs.cmu.edu>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 39

> Although I don't know the details, from what I have heard the DEC-20 suffers
> from a similar problem.

Suffers is a strong word, and it wasn't a problem.  Remember, the machine
was around years before C was invented.  I think you are saying that any
machine that punishes violation of strict pointer typing is broken.

> Wordsize is 36 bits, I think all pointers are 18-bits
> and chars can not be packed to have a pointer to them.

If this is true, you are talking about a brain-damaged C compiler.   A
pointer can be 18 bits, but REAL pointers are 36 bits and they can
point to any arbitrary byte in a word.

Probably the most unfortunate feature of the pointer structure is that
it doesn't happen to fit accepted C coding idioms.  The hardware works
best if a byte copy loop is written as

	while (*++op = +++ip);

when we all know that the "correct" (i.e. VAX order) way to do it is

	while (*op++ = +ip++);

What does all this prove about the "goodness" or "badness" of the
machine?  Nothing!  It was a clean, RISK-like architecture that was a
joy to program.  But people don't program in assembly much any more and
the idioms for the machine don't happen to map into ones that are
favored in current high-level languages.  The machine was a victim
of culture drift.

Perhaps we should be taking courses in the history of design, with proper
attention given to the cultural forces that lead to design decisions.
-- 

Griff Smith	AT&T (Bell Laboratories), Murray Hill
Phone:		(201) 582-7736
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