From: Simon Wright <simon@pushface.org>
Subject: Re: AI12-0218: What is the portable representation clause for processing IETF packets on little-endian machines?
Date: Sat, 12 May 2018 08:08:40 +0100
Date: 2018-05-12T08:08:40+01:00 [thread overview]
Message-ID: <lypo21ic5j.fsf@pushface.org> (raw)
In-Reply-To: pd53hv$g7j$1@dont-email.me
"Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org> writes:
> On 05/11/2018 11:39 PM, Simon Wright wrote:
>>
>> whereas Ada2012 says
>>
>> "To convert a record from one representation to another, two
>> record types with a common ancestor type need to be declared,
>> with no inherited subprograms."
>>
>> which seems to require _three_ types.
>
> The example in 13.6 shows this with only 2 types. This is because a
> type is defined to be its own ancestor (ARM 3.4.1).
I saw the example. I stand by my statement that it's confusing.
Perhaps there needs to be a way to mark a language usage as
domain-specific rather than natural; in English, I am not my own
ancestor (or descendant).
>> But in any case your code doesn't answer my question: what
>> representation trick could convert between
>>
>> type T is record
>> J : Integer;
>> end T;
>>
>> and
>>
>> type BE_T is new T;
>> for BE_T use record
>> ?????
>> end record;
>
> I was showing how to use records with representations to get the
> compiler to do byte swapping for you. There's no way to use them to
> change the byte order of an integer type directly.
Not quite the same, but I think I showed upthread a conversion that does
this:
function To_Fixed_32_16 (S : Four_Byte_Slice) return Fixed_32_16 is
function Convert is new Ada.Unchecked_Conversion (Four_Byte_Slice,
Fixed_32_16);
begin
if Big_Endian then
return Convert (S);
else
return Convert ((1 => S (4),
2 => S (3),
3 => S (2),
4 => S (1)));
end if;
end To_Fixed_32_16;
Of course, in C you'd use ntohl(), but we'd have to wrap something like
the above in a generic.
next prev parent reply other threads:[~2018-05-12 7:08 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-10 17:45 AI12-0218: What is the portable representation clause for processing IETF packets on little-endian machines? Dan'l Miller
2018-05-10 19:24 ` Dan'l Miller
2018-05-10 20:32 ` Paul Rubin
2018-05-10 22:24 ` Dan'l Miller
2018-05-10 22:44 ` Niklas Holsti
2018-05-10 23:14 ` Paul Rubin
2018-05-11 2:38 ` Dan'l Miller
2018-05-11 7:55 ` Simon Wright
2018-05-11 12:11 ` Lucretia
2018-05-11 13:49 ` Simon Wright
2018-05-11 16:11 ` Jeffrey R. Carter
2018-05-11 16:48 ` Simon Wright
2018-05-11 19:08 ` Jeffrey R. Carter
2018-05-11 21:39 ` Simon Wright
2018-05-11 21:56 ` Jeffrey R. Carter
2018-05-12 7:08 ` Simon Wright [this message]
2018-05-12 7:53 ` Jeffrey R. Carter
2018-05-14 22:43 ` Randy Brukardt
2018-05-11 13:46 ` Simon Wright
2018-05-11 22:12 ` Randy Brukardt
2018-05-12 10:33 ` Björn Lundin
2018-05-12 13:08 ` Simon Wright
2018-05-12 14:21 ` Björn Lundin
2018-05-10 23:07 ` Paul Rubin
2018-05-11 0:14 ` Dan'l Miller
2018-05-11 0:30 ` Paul Rubin
2018-05-11 0:50 ` Dan'l Miller
2018-05-11 1:34 ` Paul Rubin
2018-05-11 2:11 ` Dan'l Miller
2018-05-11 22:32 ` Randy Brukardt
2018-05-11 8:02 ` Simon Wright
2018-05-11 22:14 ` Randy Brukardt
2018-05-10 19:28 ` Simon Wright
2018-05-10 22:40 ` Randy Brukardt
2018-05-10 22:50 ` Dan'l Miller
2018-05-11 22:00 ` Randy Brukardt
2018-05-12 1:15 ` Paul Rubin
2018-05-14 22:54 ` Randy Brukardt
2018-05-15 0:43 ` Paul Rubin
2018-05-15 21:39 ` Randy Brukardt
2018-05-15 0:44 ` Dennis Lee Bieber
2018-05-11 8:09 ` Simon Wright
2018-05-10 19:34 ` Dmitry A. Kazakov
2018-05-10 20:06 ` Dan'l Miller
2018-05-10 22:44 ` Paul Rubin
2018-05-10 22:50 ` Randy Brukardt
2018-05-11 9:40 ` Niklas Holsti
2018-05-11 11:40 ` Dan'l Miller
2018-05-11 20:16 ` Niklas Holsti
2018-05-11 9:40 ` Dmitry A. Kazakov
2018-05-11 14:21 ` AdaMagica
2018-05-26 16:15 ` Dan'l Miller
2018-05-26 19:02 ` AdaMagica
2018-05-26 21:01 ` Dan'l Miller
2018-05-27 14:58 ` AdaMagica
2018-05-27 18:03 ` Simon Wright
2018-05-29 22:17 ` Randy Brukardt
2018-05-30 6:39 ` Simon Wright
2018-05-30 7:25 ` Dmitry A. Kazakov
2018-05-30 15:01 ` Simon Wright
2018-05-30 15:59 ` Dan'l Miller
2018-05-30 19:38 ` Randy Brukardt
2018-05-27 18:04 ` Dan'l Miller
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