Date: Fri, 3 Apr 1998 19:21:10 -0800 (PST) From: Doug White <dwhite@gdi.uoregon.edu> To: xiaominy@newton.ccs.tuns.ca Cc: freebsd-questions@FreeBSD.ORG, ifair@newton.ccs.tuns.ca, Larry.Hughes@StMarys.ca Subject: Re: bit and byte alignment on FreeBSD? Message-ID: <Pine.BSF.3.96.980403191934.11299N-100000@gdi.uoregon.edu> In-Reply-To: <352594BA.2E58B3B8@tuns.ca>
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On Fri, 3 Apr 1998, Xiaomin Ye wrote:
> Dear Sir/Madam,
> We encountered a strange problem while using FreeBSD.
> The following structure can be compacted to be 8 bytes by means of cc
> compiler on Open-VMS platform. But on FreeBSD, 12 bytes will be formed.
Well, checking this between an Alpha and an Intel is comparing apples and
oranges. They're completely different processors.
> #pragma nomember_alignment
>
> struct example_structure
> {
> unsigned type : 3;
> unsigned c : 1;
> signed mem1 : 12;
> signed mem2 : 24;
> signed mem2 : 24;
> };
>
> It seems that on FreeBSD the compiler can only provide one, two or
> four bytes alignment,
> "type" occupies 1 byte, "c" occupies 1, "mem1" 2 , "mem2" 4 bytes and
> "mem3" 4 bytes, because is no bit alignment and 3-byte alignment.
> However, on Open-VMS the compiler can provide the bit alignment,
> "type", "c" and "mem1" take 2 byte space, and "mem2", "mem3" will occupy
> 3 bytes respectively. The total space will be only 8 bytes.
> Is there any solution to this problem? Your kind will be very much
> appreciated.
The Intel architecture may not allow this type of alignment. I think
most everything has to be word-aligned anyway, so it'll be expanded.
Others are encouraged to point out my lack of knowledge of Intel processor
specifics. :)
Doug White | University of Oregon
Internet: dwhite@resnet.uoregon.edu | Residence Networking Assistant
http://gladstone.uoregon.edu/~dwhite | Computer Science Major
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