Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!usc!snorkelwacker!apple!sun-barr!newstop!sun!stpeter!cmcmanis
From: cmcmanis@stpeter.Sun.COM (Chuck McManis)
Newsgroups: comp.sys.amiga.tech
Subject: Re: The Long Align Struct Macro D_S
Keywords: Long word align, diskInfo struct BCPL
Message-ID: <132194@sun.Eng.Sun.COM>
Date: 23 Feb 90 21:39:13 GMT
References: <1990Feb19.151157.21042@csmil.umich.edu>
Sender: news@sun.Eng.Sun.COM
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 33

In article <1990Feb19.151157.21042@csmil.umich.edu> root@csmil.umich.edu writes:
>A few weeks ago somone posted a little macro that could be used in place of 
>the AllocMem() function to long align structures for use with Amigados commands
>like Examine. I lost my copy of this macro when I upgraded to Manx 5.0 
>If you have a copy or remember it, I would be most greatful. 

I don't think it was me, but the technique I use occasionally is as follows:

/* Find the size of something in words (guaranteed alignment) */
#define WORDSIZE(s)     (((s)+1)/sizeof(short) + 1)

/* Align it to a long word boundary */
#define ALIGNED(a) ((((long)(a) & 3) == 0) ? (a) : (long)(a) + 2)
 
The first macro will always get one more word of memory than you actually
need, this allows for the array to be aligned on an odd word. If we shift
our pointer by one word we will still have enough space for our structure
or whatever. To use in a program do something like this ...

/* Get enough space for a FileInfoBlock structure + 1 word */
short	buf[WORDSIZE(sizeof(struct FileInfoBlock))];

struct FileInfoBlock	*fi = ALIGNED(buf);

/* Assign fi to the long word aligned address of buf (either &buf[0] or
 * a &buf[1].
 */


--Chuck McManis
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