Representation clauses and alignment in GNAT

Representation clauses and alignment in GNAT

[Andreas Schulz]

Trying to write some code to evaluate a binary data file in 'the Ada
way' (i.e. avoiding 'and 2#0001111110000# / 2**4), I ended up with a
hierarchy of variant records with representation clauses down to
bit level, squeezed into 32 bits. The package compiled fine with
Verdix Ada, but with GNAT I get several compilation errors
'fields of "xxx_REC" must start at storage unit boundary' for the
toplevel records. Looking closer, GNAT apparently complains when
xxx_REC is a variant record, but feels OK when xxx_REC is a plain
record.

I tried to get some more insight on this topic from the GNAT
reference manual, but all I found was 13.3(32) :
An implementation need not support specific alignments...
- Followed -

So, what's 'Followed'?
- We don't have to, so we don't ?
- We don't have to, but we do (better) ?

Andreas Schulz

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