Re: bit numbers in packed arrays of Boolean

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Tue, 31 Aug 2010 13:14:48 +0200, Stephen Leake  
<stephen_leake@stephe-leake.org> a écrit:
> LRM 13.9(5) says Bit_Array_16_Type and Unsigned_16 have the same
> representation, but it does not specifically address the index order.
At least ARM 3.6 Array Types does not states anything. But as you used  
Unchecked_Conversion, it is unlikely to be portable or this result could  
be enforced. Let say this is the result of a compiler with descent default  
behaviors.

ARM 13.9 Unchecked Type Conversions says:

    11.a/2  Implementation defined: The effect of unchecked conversion for
    instances with nonscalar result types whose effect is not defined by
    the language.

And do not believe the reference defines anything for an array of 16  
bit-layout booleans.

Possibly depends on how the index is interpreted: as an index in the  
polynomial representation of the word value or as a bit index ? Both would  
be legitimate for a compiler.

That was my humble opinion on the topic.


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