Path: utzoo!utgpu!water!watmath!clyde!cbosgd!ihnp4!laidbak!daveb
From: daveb@laidbak.UUCP (Dave Burton)
Newsgroups: comp.lang.c
Subject: Re: register unions
Keywords: registers, unions
Message-ID: <1338@laidbak.UUCP>
Date: 16 Feb 88 04:23:42 GMT
References: <1229@eneevax.UUCP>
Reply-To: daveb@laidbak.UUCP (Dave Burton)
Distribution: comp.lang.c
Organization: is pretty bad/My method of
Lines: 31

In article <1229@eneevax.UUCP> noise@eneevax.umd.edu.UUCP (Johnson Noise) writes:
|	typedef union
|	{
|		char b;
|		short w;
|		long l;
|	} dreg;
|
|	typedef union
|	{
|		char *b;
|		short *w;
|		long *l;
|	} areg;
|
|	register dreg d0, d1, d2;
|	register areg a0, a1;
|
|which would effectively allow full use of cpu registers.  Note the
|similarity to 68k assembly. 

Though not specifically disallowed in the original specification of C,
this declaration is not useful in the manner you propose. K&R (pg 197)
and H&S (pg 109) state that storage is allocated from the beginning of the
union. The 68k series put the char type in the LSB, while the union
declarations want the char type in the MSB.
-- 
--------------------"Well, it looked good when I wrote it"---------------------
 Verbal: Dave Burton                        Net: ...!ihnp4!laidbak!daveb
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