Path: utzoo!utgpu!water!watmath!clyde!rutgers!umd5!brl-adm!husc6!sri-unix!quintus!ok
From: ok@quintus.UUCP (Richard A. O'Keefe)
Newsgroups: comp.lang.c
Subject: Re: register unions
Keywords: registers, unions
Message-ID: <677@cresswell.quintus.UUCP>
Date: 22 Feb 88 04:26:23 GMT
References: <1229@eneevax.UUCP> <7258@brl-smoke.ARPA> <604@mcrware.UUCP>
Distribution: comp.lang.c
Organization: Quintus Computer Systems, Mountain View, CA
Lines: 23

In article <604@mcrware.UUCP>, jejones@mcrware.UUCP (James Jones) writes:
> The place I can see people wanting unions to live in registers is something
> like
> register union {
> 	woof	*wp;
> 	char	*cp;
> 	...
> }	mumble;
Last time I looked at a PR1ME C manual, most pointers were 32 bits,
but character pointers were 48 bits.  The P400 (the machine I used)
has 32-bit registers.  {There are also the "Field Address" and
"Field Length" registers, one set of which overlaps a floating-point
register...}

If you really need to do this, you can manage it with casts.
The cast version is a wee bit better than the union version,
because Lint will complain about the casts, but the union code
will just quietly do something surprising.

	for (times = 100; --times >= 0; ) {
	    fprintf(stderr, "Byte addressing is not universal.\n");
	    fprintf(stderr, "Pointers may come in different sizes.\n\n");
	}