RE: RPG400-L Digest V2 #357

["Sims, Ken" <KSIMS@xxxxxxxxxxxxxxxx>]

Hi Peter -

>The V4R4 RPG ILE manual says:
 ...
>The position they're talking about is the position of the subfield within a
>data structure, so if the above is true, one would have to assume that the
>data structure begins on a 16-byte boundary. It would be nice if they
>explicitly said that, and assured us it won't change from release to
>release.

Based on my experimentation, since the compiler rejects pointers defined
with from/to positioning that is not on a 16-byte boundary, it appears that
data structures with pointers are always aligned on a 16-byte boundary.
Only pointer fields *have* to be aligned on a 16-byte boundary.  No other
fields *have* to be aligned on any particular boundary, and no other fields
need a 16-byte alignment for best performance; therefore there is nothing to
imply that any data structure not containing pointers is aligned on a
16-byte boundary.

The data structure being discussed in this thread does not contain actual
pointer fields since it is an externally described data structure using
character fields to hold pointers, therefore there is no reason to assume
any particular alignment.

The use of the ALIGN keyword does not imply changing the data structure
itself to ANY particular byte alignment, only to adding padding between
individual fields in the data structure to align float, signed integer, and
unsigned integer fields for performance.

Ken
Southern Wine and Spirits of Nevada, Inc.
Opinions expressed are my own and do not necessarily represent the views of
my employer or anyone in their right mind.

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