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Newsgroups: comp.lang.ada
Date: Fri, 11 May 2018 04:40:17 -0700 (PDT)
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Subject: Re: AI12-0218: What is the portable representation clause for
 processing IETF packets on little-endian machines?
From: "Dan'l Miller" <optikos@verizon.net>
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Xref: reader02.eternal-september.org comp.lang.ada:52264
Date: 2018-05-11T04:40:17-07:00
List-Id: <comp.lang.ada>

On Friday, May 11, 2018 at 4:40:19 AM UTC-5, Niklas Holsti wrote:
> On 18-05-11 01:50 , Randy Brukardt wrote:
>=20
> > Portable representation clauses are a waste of time, especially as mach=
ines
> > are inconsistent in the ways that they number bits. Just don't go there=
.
> > (218 solves one such problem, but there are many others.)
>=20
> The ability to specify Bit_Order for record representations is very=20
> useful to me, as it allows my programs to be executed both on the target=
=20
> HW (big-endian SPARC) and on the development workstations (little-endian=
=20
> x86) with exactly the same HW-level input and output.
>=20
> So thank you, ARG, for this!
>=20
> There are some gotchas and limitations (most severe is the inability to=
=20
> specify the ordering of the components of packed arrays within records)=
=20
> but on the whole it works.
>=20
> My current project has 115 cases of "for ...'Bit_Order use ...".
>=20
> (And about three cases of having to manually expand packed arrays into=20
> individual record components because of the inability mentioned above.)
>=20
> --=20
> Niklas Holsti
> Tidorum Ltd
> niklas holsti tidorum fi
>        .      @       .

Please provide an example of a Bit_Order-based-representation-clause record=
 that is portable between SPARC and IA-32/AMD64 (that is not utilizing the =
GNAT feature in A12-0218, and completely ignoring the packed-array troubles=
ome case).  There is a perennial debate whether the =E2=80=A2proper=E2=80=
=A2 usage of Bit_Order on =E2=80=A2bug-free=E2=80=A2 representation clauses=
 in an Ada compiler already solves the entire topic of A12-0218, making moo=
t A12-0218 and GNAT's already-extant feature therein.  Your long 115-cases =
track-record of success with Bit_Order representation for endianness portab=
ility between SPARC and IA-32/AMD64 seems to not only concur, but strongly =
contains the wisdom necessary to decisively blow A12-0218 out of the water.=
  Please clearly lead us; please clearly teach us how to utilize Bit_Order =
properly.