Re: RPG400-L Digest V2 #357

["Peter Dow" <pcdow@xxxxxxxxxxxxxxx>]

Hi Ken,

How can one tell what boundary a data structure, or any other field for that
matter, is aligned on?

Curious,
Peter Dow
Dow Software Services, Inc.
909 425-0194 voice
909 425-0196 fax

----- Original Message -----
From: "Sims, Ken" <KSIMS@SOUTHERNWINE.com>
To: <rpg400-l@midrange.com>
Sent: Tuesday, October 10, 2000 10:08 AM
Subject: RE: RPG400-L Digest V2 #357


> 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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