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From: Andy <andy@nospam.com.tj>
Subject: Re: Sequential_IO Data Portability
Date: 2000/02/01
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Date: 2000-02-01T12:47:16+00:00
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> Nick Roberts wrote:
 
> Being able to use another compiler (ie GNAT95) in the same manner without having to expend vast amounts
> of effort on translating or rep spec'ing file formats (which would be tedious and error prone) means we
> could concentrate our resources on system improvements.
> 
> So that's the background. If anyone has any practical experience (positive or negative) of sharing binary
> files between Linux, LynxOs, SCO and/or Windows NT using GNAT95 I would be delighted to hear from you.
> 
The project I work on does not share files, but we do share binary data
(via messages) between
a number of DEC Alpha platforms (using Rational Apex) and VME 68k
platforms (using a Greenhills
compiler). In the end we deceided to bite the bullet and rep spec all
the messages (and closure 
of the all the types used in these messages). 

To this end we have developed a tool (written in shell scripts & Perl)
to auto generate the rep 
specs. The rep specs are such that they are evaluated at compile time.
Thus if a low level type
changes, say from scalar to a physically larger/smaller scalar, or to a
composite type, then the 
rep specs of the types dependent upon this type are automatically
adjusted at compile time (by 
both compilers).

While I cannot provide the scripts or the Perl (they are designed to
work within an Apex
environment anyway) I could provide more info on the compile time
arithmetic we perform in
order to generate the rep specs if required. 

(we also have to perform endian conversions, but that's another story).
 
___________________________________________

Andy Starritt
___________________________________________