Hello,
What is equivalent of __unaligned attribute in GNU C?
I've searched for some time and it seems that it just does not exist...
/*
For HP and new Microsoft compilers it works this way:
long_pointer = (some unaligned address)
long_value = (* (__unaligned long *) long_pointer );
This causes the compiler to emit code that gets the value
in some slow but sure way, but avoiding exceptions
*/
No need to suggest workarounds please...
Regards
--PA
18  10077 
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Hash: SHA1
"Pavel A." <pa*****@NOwrit emeNO.com> writes: What is equivalent of __unaligned attribute in GNU C?
I've searched for some time and it seems that it just does not exist...
It appears not to. That's probably because it should not be needed
unless your code is buggy. If your code is standard C, the compiler
should have aligned everything nicely for you. However, you didn't
post the code that creates the unaligned pointer.
Also:
- - Some CPUs allow unaligned access.
- - Some operating systems can transparently handle unaligned access on
systems that don't support it.
- --
Roger Leigh
Printing on GNU/Linux? http://gimp-print.sourceforge.net/
Debian GNU/Linux http://www.debian.org/
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[fu-t set]
in comp.lang.c i read: What is equivalent of __unaligned attribute in GNU C?
I've searched for some time and it seems that it just does not exist...
correct -- there is nothing standard.
--
a signature
Thanks Roger for your reply.
I was looking how to implement functions like LoadUnalignedLo ng /
StoreUnalignedL ong
(the need for these is obvious... if you get unaligned structure from file
or network etc).
So will do it anyway else.
--PA
"Roger Leigh" <${*******@inva lid.whinlatter. ukfsn.org.inval id> wrote in
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Hash: SHA1
"Pavel A." <pa*****@NOwrit emeNO.com> writes:
What is equivalent of __unaligned attribute in GNU C?
I've searched for some time and it seems that it just does not exist...
It appears not to. That's probably because it should not be needed
unless your code is buggy. If your code is standard C, the compiler
should have aligned everything nicely for you. However, you didn't
post the code that creates the unaligned pointer.
Also:
- - Some CPUs allow unaligned access.
- - Some operating systems can transparently handle unaligned access on
systems that don't support it.
- --
Roger Leigh
Printing on GNU/Linux? http://gimp-print.sourceforge.net/
Debian GNU/Linux http://www.debian.org/
GPG Public Key: 0x25BFB848. Please sign and encrypt your
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MDJleeQZG8u63b7 TJZExNog=
=XMLL
-----END PGP SIGNATURE-----
"Pavel A." wrote:
I was looking how to implement functions like LoadUnalignedLo ng /
StoreUnalignedL ong (the need for these is obvious... if you get
unaligned structure from file or network etc).
So will do it anyway else.
Please don't toppost. It is not acceptable in c.l.c. See sig
below.
There is no such need. How do you get an "unaligned structure"?
All you can receive from a network of file is some gestalt of
bytes, which should have a defined relationship to a field in a
structure. The details of a structure are not valid outside the
system that created it, and can be freely changed, even by a
compiler upgrade.
--
Some informative links:
news:news.annou nce.newusers http://www.geocities.com/nnqweb/ http://www.catb.org/~esr/faqs/smart-questions.html http://www.caliburn.nl/topposting.html http://www.netmeister.org/news/learn2quote.html
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"Pavel A." <pa*****@NOwrit emeNO.com> writes:
[Please don't top-post] I was looking how to implement functions like LoadUnalignedLo ng /
StoreUnalignedL ong
(the need for these is obvious... if you get unaligned structure from file
or network etc).
I've never seen those non-standard functions. Due to the hideous
naming, I assume they come from MS Windows?
The need for them aside, you could always memcpy to a known aligned
memory location before reading/writing. It should be fairly cheap,
but still less than ideal. If your software is properly written, you
simply won't have alignment issues.
- --
Roger Leigh
Printing on GNU/Linux? http://gimp-print.sourceforge.net/
Debian GNU/Linux http://www.debian.org/
GPG Public Key: 0x25BFB848. Please sign and encrypt your mail.
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TKSkV3oERlS9U9D F21grf60=
=BlzH
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Roger Leigh <${*******@inva lid.whinlatter. ukfsn.org.inval id> wrote: "Pavel A." <pa*****@NOwrit emeNO.com> writes:
[Please don't top-post]
I was looking how to implement functions like LoadUnalignedLo ng /
StoreUnalignedL ong
(the need for these is obvious... if you get unaligned structure from file
or network etc).
I've never seen those non-standard functions. Due to the hideous
naming, I assume they come from MS Windows?
You'd say so, but AFAICT not even that.
The need for them aside, you could always memcpy to a known aligned
memory location before reading/writing. It should be fairly cheap,
but still less than ideal.
If you have a halfway decently defined network or file format, you won't
be reading directly into your objects if that's impossible. You'll be
manipulating the byte _values_, rather than their representations in
memory.
Richard
On Thu, 19 May 2005 19:56:17 +0100, Roger Leigh wrote: -----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
"Pavel A." <pa*****@NOwrit emeNO.com> writes:
What is equivalent of __unaligned attribute in GNU C?
I've searched for some time and it seems that it just does not exist...
It appears not to. That's probably because it should not be needed
unless your code is buggy.
I respectfully disagree: In networking applications, for performance
reasons (to avoid data copying) one must frequently deal with portions of
buffers that are not correctly aligned.
Thomas Carter wrote: On Thu, 19 May 2005 19:56:17 +0100, Roger Leigh wrote:
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"Pavel A." <pa*****@NOwrit emeNO.com> writes:
What is equivalent of __unaligned attribute in GNU C?
I've searched for some time and it seems that it just does not exist...
It appears not to. That's probably because it should not be needed
unless your code is buggy.
I respectfully disagree: In networking applications, for performance
reasons (to avoid data copying) one must frequently deal with portions of
buffers that are not correctly aligned.
That depends on what you mean by unaligned. The C standards don't allow
the kinds of type punning which would place, for example, a long long
int at an odd short int address. Code which does so is non-portable.
Even Microsoft C, in the newer 64-bit versions, gets away from the
requirement to maximize support of 64-bit data located on any 32-bit
boundary, but this NG is about standard C.
If you mean, for example, a string of ints starting at any legal int
boundary, that's the default, and doesn't require any attribute or
pragma. gcc does support specification of higher alignments, such as
those which would allow the use of aligned pair load and store instructions.
On Sat, 18 Jun 2005 14:50:47 +0000, Thomas Carter wrote: On Thu, 19 May 2005 19:56:17 +0100, Roger Leigh wrote:
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Hash: SHA1
"Pavel A." <pa*****@NOwrit emeNO.com> writes:
What is equivalent of __unaligned attribute in GNU C?
I've searched for some time and it seems that it just does not exist...
It appears not to. That's probably because it should not be needed
unless your code is buggy.
I respectfully disagree: In networking applications, for performance
reasons (to avoid data copying) one must frequently deal with portions of
buffers that are not correctly aligned.
This is a generalisation which is the for most part wrong. Not totally
wrong but still mostly wrong. However a discussion of why is beyond the
scope of comp.lang.c (i.e. where I am reading this).
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