Re: Assembler: alignment of machine instructions

In article <VPSdnXoSaKoDpnrf4p2dnA@[EMAIL PROTECTED]
>,
Sven Pran <no.direct@[EMAIL PROTECTED]
> wrote:
> ...
>
>Do you also know and understand the difference between
>
>XXX DS 0H
>
>and
>
>XXX DC 0H'0' ?
>
>There is a significant difference (although normally not very im****tant).
>
>regards Sven
>

The first example merely resets the location counter for the
next generated output in the object deck.  If the "DS 0H"
should bump the location counter to a halfword alignment, the
extra byte is uninitialized data in the object deck.

The second example conditionally generates an extra byte to
align to the next halfword as if it were a DC.  The object
deck will contain any forced alignments initialized with needed
bytes set to X'00'.

The second technique for generating labels in a macro was once
preferred because it could generate object decks with fewer records
(because the location counter wasn't being reset) and because
the extra padding for alignments would be initialized in the
object deck.  Neither benefit is im****tant today, but it was
once a [very] small concern.