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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Stream_Element_Array
Date: Thu, 15 Sep 2011 22:42:03 +0100
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Date: 2011-09-15T22:42:03+01:00
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Alexander Korolev <antonovkablog@gmail.com> writes:

> On Sep 16, 12:11 am, Simon Wright <si...@pushface.org> wrote:
>> Alexander Korolev <antonovkab...@gmail.com> writes:
>> > My confusion is about the order of the Stream_Element for the cases I
>> > posted
>>
>> That has to depend on what the thing at the other end is expecting!
>>
>> If there's no proper specification, do you maybe have some C code that
>> we could help to work it out from?
>
> It expecting 2 byte Lenth: |192|lenght (MSB)|Lenth (LSB)|Data|
> checksum|
> " The message length is a 2-byte field (MSB) equal to the size of the
> data field and checksum
> before byte stuffing has been executed" - from the doc

I don't know what they mean by (MSB) in "a 2-byte field (MSB)".

That said, it seems pretty clear that the first byte on the wire is to
be the most significant byte of Length : Unsigned_16, so you want
somthing like

   Write (Length / 256);
   Write (Length and 255);

or maybe

with Ada.Text_IO; use Ada.Text_IO;
with Interfaces;
procedure Streaming is

   procedure Write (B : Interfaces.Unsigned_8) is
   begin
      Put_Line ("b => " & Interfaces.Unsigned_8'Image (B));
   end Write;

   V : Interfaces.Unsigned_16;

   use type Interfaces.Unsigned_16;

begin

   V := 16#8180#;

   Write (Interfaces.Unsigned_8 (Interfaces.Shift_Right (V, 8)));
   Write (Interfaces.Unsigned_8 (V and 16#FF#));

end Streaming;

The output is

$ ./streaming 
b =>  129
b =>  128