Re: Modified proposals for Ada-Comment

[Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP>]

On 2014-07-12, Niklas Holsti <niklas.holsti@tidorum.invalid> wrote:
>
> Might you include in this question also whether increasing the size of
> an atomic object using a 'Size clause means that the atomic access
> should apply to all the bits included in 'Size, and not just to the bits
> included in the declared components of the object?
>

The response (from Tucker Taft) I got to your 'Size question was this:

My original question as submitted:

||    As a related question, when C.6(15) does apply, does it also apply to
||    all the bits included by 'Size when 'Size has been used to increase
||    the size of the atomic object (say from 5 bits to 32 bits) ?
||

The response:

|
|The definition of 'Size on an elementary object is that it refers to the
|number of bits normally read/written, as specified in 13.1(7/2):
|
|  "The representation of an object consists of a certain number of bits
|  (the size of the object). For an object of an elementary type, these are
|  the bits that are normally read or updated by the machine code when
|  loading, storing, or operating-on the value of the object...."
|
|For a non-atomic composite object, extra bits might not be loaded/stored,
|again quoting from that same paragraph:
|
|  "... For a composite object, padding bits might not be read or updated in
|  any given composite operation, depending on the implementation."
|
|For an atomic composite object, although it is not stated explicitly, the
|implication is that the 'Size of an atomic object determines the number of
|bits read/written indivisibly (e.g. see C.6(11/4)).

On a related matter, the responses to the C.6(15) question about if
Atomic on a record applies to it's components, are in the general
direction of no it doesn't.

Simon.

-- 
Simon Clubley, clubley@remove_me.eisner.decus.org-Earth.UFP
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