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From: Simon Wright <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: Controlling endian-ness?
Date: Tue, 12 Aug 2008 14:42:38 +0100
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Date: 2008-08-12T14:42:38+01:00
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"Peter C. Chapin" <pcc482719@gmail.com> writes:

> anon wrote:
>
>> For using Unsigned_32. Why not just override the built-in Write
>> attributes routines for Unsigned_32 by re-writing the attributes
>> routines. This may at most require a new package with a few extra
>> attributes routines that may be needed. Also, this will also allow
>> you to use "Shift_Left/Shift_Right" directly with Unsigned_32.  
>>
>> So in your program you could use:
>>
>>    Data : Unsigned_32 ;
>>   ...
>>    Unsigned_32'Write ( Stream_Pointer, Data ) ;
>
> I actually tried something like this but the compiler told me that I
> couldn't redefine attributes for that type (or something like that). I
> think the problem is that since the type is defined in another package
> it is already frozen or some such. It could also be that I did it
> wrong.

(I'm not sure if this is in GNAT-GPL-2008, which I wasn't able to build
for Intel Mac):

(1) find s-strxdr.adb in the Ada library source directory
.../adainclude/

(2) copy it to s-stratt.adb in your compilation path

(3) give gnatmake the -a flag.

s-strxdr.adb contains an alternate body for System.Stream_Attributes
which streams to/from XDR (eXternal Data Representation) format.

You might think you would only need to do this on the little-endian
side, but there was a problem with Wide_Character in older GNATs (2
bytes or 4?) so checking the source would be good. Also, of course, you
might have problems with floats: no problems found by us where it's IEE
hardware both sides, eg PowerPC/i386.