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From: "Bertrand Augereau" <baugereau@ifrance.kom>
Newsgroups: comp.lang.ada
Subject: Re: Ada The Best Language?
Date: Fri, 20 Jul 2001 15:28:25 +0200
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Date: 2001-07-20T15:28:25+02:00
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>
> Please specify the C++ Code for offset 6.
>       [...]
>       dont_fragment    at  6 range 6 .. 6;
>       more_fragments   at  6 range 5 .. 5;
>       offset1          at  6 range 0 .. 4;
>       [...]
>

If I don't get something wrong (I'm at work so I don't have much time... or
do I ;-) ):
I'm not that sure of the exact semantics of 'at position range a..b'

struct Head
{
    ...
    unsigned int offset1:5;
    unsigned int more_fragments :1;
    unsigned int dont_fragment : 1;
    unsigned int pad:1;
    ..
}

But you have to ensure the previous elements of the structure make the
padding right.
that's what I said there "(well almost exactly, you have to take care of the
offset with appropriate padding, but bitfields take care of the 'range')"

Ok this is a lame disclaimer ;-)

> Ada95 still have problems, there is no portable way to specify the layout
of
> the whole 12bit offset.
>
> >But I'm not sure of endianness consideration in both cases, especially
for
> >network code.
>
> https://www.iks-jena.de/mitarb/lutz/ada/net/net-portability__adb.htm
>
> It's horrible ugly, but compile time evaluable and the generated code is
> incredibly fine. Ever seen a Compiler generating an endian prefix on
alpha?

Sometimes you have to live with ugliness...