Re: Stream_Element_Array

[Adam Beneschan <adam@irvine.com>]

On Sep 15, 2:42 pm, Simon Wright <si...@pushface.org> wrote:
> Alexander Korolev <antonovkab...@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#));

Would it be useful to add a 'Stream_Element_Order attribute to the
language (somewhat analogous to 'Stream_Size) that would allow a
programmer to specify, via an aspect clause or attribute definition
clause, whether values of a given elementary type are read/written
with the most or least significant byte first?

                          -- Adam