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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Decoding an octet stream
Date: 1999/12/03
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 <81u247$kc3$1@hobbes2.crc.com> <87puwsmizb.fsf@deneb.cygnus.argh.org>
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Date: 1999-12-03T00:00:00+00:00
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In article <87puwsmizb.fsf@deneb.cygnus.argh.org>,
  " "@deneb.cygnus.argh.org (Florian Weimer) wrote:
> "David C. Hoos, Sr." <david.c.hoos.sr@ada95.com> writes:
>
> >       if System.Default_Bit_Order = System.Low_Order_First
then
> >          Swap (The_Bytes);
> >       end if;
>
> Does this really work?  I thought that
System.Default_Bit_Order
> hasn't got to do anything with octet ordering issues (aka
endianess).
> After all, there are more than just two methods of combining
four octets
> to a 32 bit integer (for example).

Well yes, but as we all know there are only two methods worth
bothering about. And in practice bit ordering and byte ordering
have to be the same, otherwise you get non-contiguous data
fields (this is why changing the default on bit_order, which
does NOT result in changing the byte order, is highly dubious
on a byte addressed machine, and hence not required to be
implemented).

In the latest version of GNAT we allow the non-default bit order
to be specified, but we insist that all record representation
clauses for such a record either lie within a single byte, or
correspond to an integral number of bytes (in the latter case
we warn that the byte order will NOT be modified).




>


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