Re: Little Endian -> Big Endian (Ada95 / GNAT)

["David C. Hoos" <david.c.hoos.sr@ada95.com>]

"James Amor" <jamesamor@hotmail.com> wrote in message
news:bac31daa.0402250138.fc4ed92@posting.google.com...
> Hi,
>
> At present I am writing a tool to create a file which contains various
> extracted ELF symbols. The output data structure, a list of unsigned
> 32's, is to be used as part of an image on a PowerPC target.
>
> Problem: As it is compiled on Wintel the tool is producing an output
> in little endian and PowerPC is big endian!
>
> Question: How do I modify my code to write the output in big endian
> format?

If you use Stream IO to write the data, then you can take advantage of
the solution the GNAT folks created for Distributed Systems (Annex E
of the Ada Lanuage Reference Manual).

This solution is embodied in the glade supplement to gant.

For example, if you're using gant-3.15p, the corresponding glade can
be found at ftp://ftp.cs.nyu.edu/pub/gnat/3.15p/glade

Then, replace the file s-stratt.adb in your standard gnat distribution
with the one from the same version of glade, and re-compile and
rebuild the library files (.a), and you have what you want.  Now, as
long as your types are declared the same on both platforms (with no
representation clauses) you will have platform-independence.

I'm not sure why GNAT didn't do this from the beginning -- perhaps because
they didn't provide an implementation of the Distributed Systems Annex at
the beginning.  Also, there is a small performance penalty paid for
shuffling bits around to achieve platform independence.

Hope this helps.