Re: AI12-0218: What is the portable representation clause for processing IETF packets on little-endian machines?

["Dan'l Miller" <optikos@verizon.net>]

On Friday, May 11, 2018 at 4:40:19 AM UTC-5, Niklas Holsti wrote:
> On 18-05-11 01:50 , Randy Brukardt wrote:
> 
> > Portable representation clauses are a waste of time, especially as machines
> > are inconsistent in the ways that they number bits. Just don't go there.
> > (218 solves one such problem, but there are many others.)
> 
> The ability to specify Bit_Order for record representations is very 
> useful to me, as it allows my programs to be executed both on the target 
> HW (big-endian SPARC) and on the development workstations (little-endian 
> x86) with exactly the same HW-level input and output.
> 
> So thank you, ARG, for this!
> 
> There are some gotchas and limitations (most severe is the inability to 
> specify the ordering of the components of packed arrays within records) 
> but on the whole it works.
> 
> My current project has 115 cases of "for ...'Bit_Order use ...".
> 
> (And about three cases of having to manually expand packed arrays into 
> individual record components because of the inability mentioned above.)
> 
> -- 
> 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 troublesome case).  There is a perennial debate whether the •proper• usage of Bit_Order on •bug-free• representation clauses in an Ada compiler already solves the entire topic of A12-0218, making moot A12-0218 and GNAT's already-extant feature therein.  Your long 115-cases track-record of success with Bit_Order representation for endianness portability 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.