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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.unix,net.lang.c
Subject: Re: Portablity using structures and malloc - Help
Message-ID: <928@umcp-cs.UUCP>
Date: Sat, 20-Jul-85 23:31:41 EDT
Article-I.D.: umcp-cs.928
Posted: Sat Jul 20 23:31:41 1985
Date-Received: Mon, 22-Jul-85 03:57:31 EDT
References: <81@drux1.UUCP> <907@umcp-cs.UUCP> <4772@allegra.UUCP>
Organization: U of Maryland, Computer Science Dept., College Park, MD
Lines: 27
Xref: linus net.unix:4505 net.lang.c:5180

> malloc knows [the alignment constraints of the machine], but it's
> a pity that you can't make malloc tell.  If there were a nice
>
>   int malign() {return ALIGNMENT_MULTIPLE;}

True.  However, there is a general rule you can use that I've not
yet seen fail on any machine: align your object on an ``n'' bit
boundary, where ``n'' is the smallest power of 2 that is not less
than the size of the object you're allocating.  (Of course this
can be quite wasteful for large areas....)

In case what I wrote doesn't say what I really meant, here's an
example:

	int malign(size)
	register int size;
	{
		register int n = 0;

		while ((1 << n) < size)
			n++;
		return (1 << n);
	}
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 4251)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@maryland