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From: "Eric G. Miller" <egm2@jps-nospam.net>
Subject: Re: Last stream problem: byte order
Newsgroups: comp.lang.ada
Message-ID: <pan.2002.03.25.20.33.30.870308.29435@jps-nospam.net>
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Date: Tue, 26 Mar 2002 04:32:43 GMT
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In <mailman.1017085322.10332.comp.lang.ada@ada.eu.org>, Erik Sigra wrote:

> Now my stream application almost works. The last remaining problem seems to 
> be byte order. The server is programmed in C++ with Qt and the client is 
> programmed in Ada with adasockets-1.0. The last thing I did was to change the 
> byte order in the server 
> ("the_stream.setByteOrder(QDataStream::LittleEndian);"). After that the 
> numbers came out right at the other end.
> 
> However, this may not be a safe solution. The safe way would probably be to 
> always have the network communication in BigEndian format and make sure the 
> client always obeys this, regardless of the platform.
> 
> So how does one set the byte order to BigEndian on the Ada side? Or is there 
> a different, better idea?

Up to you to decide when and what order, but the following type of thing
could be used by read/write routines...

with Ada.Unchecked_Conversion;
package  Byte_Swap is

	type Bits8  is mod 2**8;

	type Two_Byte is 
	   record
	      A : Bits8;
	      B : Bits8;
	   end record;

	for Two_Byte use
	   record
	      A at 0*2 range 0 .. 7;
	      B at 0*2 range 8 .. 15;
	   end record;

        function To_Two_Byte is new
		Ada.Unchecked_Conversion (Source => Short_Integer,
		                          Target => Two_Byte);
        function To_Short is new
 		Ada.Unchecked_Conversion (Source => Two_Byte,
                                          Target => Short_Integer);
-- etc ...

        procedure Swap (data : in out Two_Byte);

-- etc ...

package body Swap_Bytes is

        procedure Swap (data : in out Two_Byte) is
		tmp : Bits8;
	begin
		tmp    := data.A;
	        data.A := data.B;
                data.B := tmp;
	end Swap;

-- etc ...