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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Does Ada support endiannes?
Date: Mon, 12 Dec 2011 14:22:39 +0100
Organization: cbb software GmbH
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Date: 2011-12-12T14:22:39+01:00
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On Mon, 12 Dec 2011 04:46:22 -0800 (PST), Gerd wrote:

> On 12 Dez., 12:27, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
> wrote:
> 
> Any suggestion on how to convert, others than using "/" and "mod"?

Why not to use them? It would be a bad idea trying to avoid them.

It won't give you much performance, because memory mapping would require
unpacking, alignment, checksum evaluation, stuff which would turn into
extra copying. So why not just:

   type Octet is new Unsigned_8;
   type Word is new Unsigned_16;
   type Octet_Array is array (Positive range <>) of Octet;

   procedure Get_Little_Endian (Data : Octet_Array; Index : in out Integer;
      Value : out Word) is -- No extra copying
   begin
      Value := Word (Data (Index)) + Word (Data (Index + 1)) * 256;
      Index := Index + 2;
   end Get_Little_Endian;

Arithmetic is cheap. Memory access is expensive.

Note also, that a real-life protocol could also have specially encoded
values reserved for indication of status (overflow, underflow etc). So
memory mapping would not work anyway.

P.S. We are developing hard real-time communication applications handling
various quite weird hardware protocols. Believe or not, we are using no
representation clauses at all.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de