From: "Randy Brukardt" <randy@rrsoftware.com>
Subject: Re: Using representation clauses in networking software
Date: Mon, 16 Aug 2010 22:32:41 -0500
Date: 2010-08-16T22:32:41-05:00 [thread overview]
Message-ID: <i4cvst$dei$1@munin.nbi.dk> (raw)
In-Reply-To: 8762zbhnhy.fsf@mid.deneb.enyo.de
"Florian Weimer" <fw@deneb.enyo.de> wrote in message
news:8762zbhnhy.fsf@mid.deneb.enyo.de...
>* Simon Wright:
>
>> I haven't tried it but
>> .. http://www.adaic.com/standards/05rm/html/RM-13-5-3.html
>
> This only affects the interpretation of bit positions. It does not
> change the memory layout of components.
When we discussed this the last time, it was concluded that supporting out
of order byte reads (especially those for unusual numbers of bits) is just
too expensive for implementations for the relatively small amount of use
that they would get. Moreover, such things could not be volatile or atomic
on most hardware (because they would require multiple reads/writes of the
various pieces - the pieces wouldn't necesssarily be contiguous in memory
for the non-native format), so they couldn't be used for hardware
interfaces. That would eliminate half of the potential uses.
Remember that read/writes of memory are probably the most fundamental thing
that a compiler does; supporting split reads would require changes to
virtually every part of a compiler. (For Janus/Ada, we would have to add
intermediate code instructions to support such reads, with costs in
everything that handles intermediate code and target code generation.)
Randy.
next prev parent reply other threads:[~2010-08-17 3:32 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-15 11:33 Using representation clauses in networking software Florian Weimer
2010-08-15 13:44 ` Yannick Duchêne (Hibou57)
2010-08-15 14:32 ` Dmitry A. Kazakov
2010-08-15 14:44 ` Florian Weimer
2010-08-15 15:04 ` Dmitry A. Kazakov
2010-08-15 15:32 ` Florian Weimer
2010-08-15 16:10 ` Dmitry A. Kazakov
2010-08-15 16:40 ` Yannick Duchêne (Hibou57)
2010-08-15 17:58 ` Dmitry A. Kazakov
2010-08-15 19:11 ` Shark8
2010-08-15 19:15 ` Simon Wright
2010-08-15 20:25 ` Maciej Sobczak
2010-08-15 21:24 ` Simon Wright
2010-08-16 6:40 ` Dmitry A. Kazakov
2010-09-04 20:46 ` Florian Weimer
2010-08-15 15:39 ` Yannick Duchêne (Hibou57)
2010-08-15 15:31 ` Yannick Duchêne (Hibou57)
2010-08-15 15:30 ` Yannick Duchêne (Hibou57)
2010-08-15 16:10 ` Dmitry A. Kazakov
2010-08-16 10:57 ` Stephen Leake
2010-08-15 15:58 ` Simon Wright
2010-08-15 16:03 ` Florian Weimer
2010-08-17 3:32 ` Randy Brukardt [this message]
2010-08-16 9:12 ` anon
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