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From: Simon Wright <simon@pogner.demon.co.uk>
Subject: Re: Fortran's Equivalence
Date: 1997/04/10
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References: <333840D1.7B12@cae.ca> <E8385t.9zE@thomsoft.com>
 <dewar.860159911@merv> <3349165C.3B93@cae.ca>
 <1997Apr8.155111.26714@nosc.mil>
 <mheaney-ya023680000804971958130001@news.ni.net>
 <334BA679.5E5D@gsfc.nasa.gov> <dewar.860617761@merv>
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Newsgroups: comp.lang.ada
Date: 1997-04-10T00:00:00+00:00
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dewar@merv.cs.nyu.edu (Robert Dewar) writes:

> Stephen says
> 
> <<Unfortunately, not even gnat implements this attribute>>
> 
> referring to the Bit_Order attribute representation clause.
> 
> Well i appreciate the implied expectation that GNAT implemnts everything :-)
> 
> But the Ada 95 language does not really expect this attribute definitoin
> to be implemented for byte addressed machines, since it results in very
> awkward non-contiguous fields.

What worked for me was

  given an interfaces.c.int to be interpreted as bit fields
  declare record type without representation
  declare variable "result" of this type
  if system.default_bit_order = system.high_order_first then
    declare derived record type with big-endian representation
    do unchecked conversion from interfaces.c.int to this type
    assign to "result"
  else
    declare derived record type with little-endian representation
    do unchecked conversion from interfaces.c.int to this type
    assign to "result"
  end if

which is long-winded but does the job! No doubt there are other ways ..

-Simon