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From: chris@umcp-cs.UUCP
Newsgroups: net.lang.c
Subject: Re: Yet another ALIGN idea.
Message-ID: <2355@umcp-cs.UUCP>
Date: Sat, 12-Jul-86 00:14:04 EDT
Article-I.D.: umcp-cs.2355
Posted: Sat Jul 12 00:14:04 1986
Date-Received: Sat, 12-Jul-86 06:22:15 EDT
References: <1038@ttrdc.UUCP> <2600066@ccvaxa>
Reply-To: chris@maryland.UUCP (Chris Torek)
Organization: University of Maryland, Dept. of Computer Sci.
Lines: 30

In article <2600066@ccvaxa> aglew@ccvaxa.UUCP writes:
>Since an alignment constant doesn't necessarily work, how about an
>alignmentof(object) operator, analagous to sizeof()? At least that'll work
>on all architectures that have alignments based on multiples.

I think this can still be implemented with a common header file, e.g.,

	#define OFFSET_TO_ALIGN(ptr)	/*something*/
	#define	IS_ALIGNED(ptr)	(OFFSET_TO_ALIGN(ptr) == 0)

On a Vax, and purely for efficiency, /*something*/ is

	#define	OFFSET_TO_ALIGN(ptr)	((4 - (int) (ptr)) & 3)

On a Pyramid, the same `define' works; on a Sun, it can be reduced to

	#define	OFFSET_TO_ALIGN(ptr)	((int) (ptr) & 1)

On your hypothetical machine, /*something*/ may be

	#define	OFFSET_TO_ALIGN(ptr)	(_offset_to_align(sizeof *(ptr)))

where _offset_to_align is a library function.

(N.B.: That it *can* be done this way does not mean that it *must*
be done this way.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu