Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!brunix!rjd
From: rjd@cs.brown.edu (Rob Demillo)
Newsgroups: comp.sys.atari.st
Subject: Help with bit field troubles in Laser C
Message-ID: <34368@brunix.UUCP>
Date: 29 Mar 90 04:33:30 GMT
Sender: news@brunix.UUCP
Reply-To: rjd@cs.brown.edu (Rob Demillo)
Organization: Brown University Department of Computer Science
Lines: 50

I have a bit (excuse the pun) of a problem I'd like some
help with.

I am bringing some C code that I wrote over from a UNIX system which 
is trying to do the following:
	set up bit fields within a 4 byte word.
	union that word to a 4 byte char string and a long.

Essentially, the structure mappings look like:

	struct phred
		{
		unsigned long	a:20;
		unsigned long	b:11;
		unsigned long	c:1;
		} ;

	union {
		struct phred	ieee;
		char		string[4];
		float		floater;
		} float_guy;

This way, when I read a floating point number into float_guy.floater,
I can get at the word in a variety of different chunks...

Now, I've ported this code to a couple of machines, and it works
fine, but, unfortunately...Laser C does not allow bit field assignments
on anything other than unsigned ints, so it chokes on by
unsigned long a:20, etc...

...looking at the K&R language description, it states as one of
the caviats that bit fields should not cross int boundaries, and
an int in Laser C is 2 bytes long. 

So, am I screwed, or can you folks suggest an alternative to what
I want to do? (I *hope* so, otherwise I'm in for a *major* rewrite of
my code, and what I'll be left with is an ST-specific peice of
C code...I hate that.

So, any suggestions?

Thanks in advance.....
	-- Rob


 - Rob DeMillo			| Internet: 	 rjd@brown.cs.edu     
   Brown University 		| Also Internet: demillo@juliet.ll.mit.edu
   Planetary Science Group	| Reality: 401-273-0804 (home)
"I say you *are* the Messiah, Lord! And I ought to know, I've followed a few!"