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From: dave@murphy.UUCP (H. Munster)
Newsgroups: comp.lang.c
Subject: machines with oddball char * formats
Message-ID: <177@houligan.UUCP>
Date: Thu, 13-Nov-86 08:58:44 EST
Article-I.D.: houligan.177
Posted: Thu Nov 13 08:58:44 1986
Date-Received: Sun, 16-Nov-86 20:20:09 EST
Organization: Gould Electronics, Ft. Lauderdale, Florida.
Lines: 37

I can think of one, from my college days: the Univac 1100 mainframes.  I have
never seen an implementation of C on one of these, but I can make a few
guesses at what it would have to do for that architecture.

First of all, the machine uses a 36-bit word size.  Normally, addressing
is done in words; a pointer to a word is a 36-bit type (of which only 18
bits are normally used, but let's not worry about that).  However, to
address anything smaller than a word, a wierd "byte pointer" format is
used; this format has an 18-bit word address field, a 3-bit field that
somehow indicates what part of the word to use (the relationship between
the value in this field and the indicated byte isn't clear to me at
all), a field that indicates the byte size, and a couple of other bits
whose functions I don't remember but which would probably not be needed. 
So, if short is 18 bits and char is 9 bits, you would have three formats
of pointers: ordinary word addresses for ints, floats, and other word-
aligned things, a byte pointer format for shorts, and another byte ptr
format for chars.  (They also have a 12-bit size, but I can't think of
any good use for it.)

A C compiler implemented in this way would have to do a lot of pointer
conversions!  Not only that, but it isn't even *possible* to cast a
short or char ptr into an int ptr if the address pointed to is not on
a word boundary.

I would like to hear from anyone who has used an actual C compiler on
one of these beasts to see if they work like what I described above.
---
It's been said by many a wise philosopher that when you die and your soul
goes to its final resting place, it has to make a connection in Atlanta.

Dave Cornutt, Gould Computer Systems, Ft. Lauderdale, FL
UUCP:  ...{sun,pur-ee,brl-bmd}!gould!dcornutt
 or ...!ucf-cs!novavax!houligan!dcornutt
ARPA: wait a minute, I've almost got it...

"The opinions expressed herein are not necessarily those of my employer,
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