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6.21 RM 13.3(50-56): Size Clauses

"If the Size of a subtype is specified, and allows for efficient independent addressability (see 9.10) on the target architecture, then the Size of the following objects of the subtype should equal the Size of the subtype:

Aliased objects (including components)."


"Size clause on a composite subtype should not affect the internal layout of components."

Followed. But note that this can be overridden by use of the implementation pragma Implicit_Packing in the case of packed arrays.

"The recommended level of support for the Size attribute of subtypes is:

The Size (if not specified) of a static discrete or fixed point subtype should be the number of bits needed to represent each value belonging to the subtype using an unbiased representation, leaving space for a sign bit only if the subtype contains negative values. If such a subtype is a first subtype, then an implementation should support a specified Size for it that reflects this representation."


"For a subtype implemented with levels of indirection, the Size should include the size of the pointers, but not the size of what they point at."