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Programming > Assembly 370 > Re: Assembler: ...
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Re: Assembler: alignment of machine instructions

by beu@[EMAIL PROTECTED] (Bruce Uttley) Jul 27, 2005 at 08:50 PM

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.
 




 13 Posts in Topic:
Assembler: alignment of machine instructions
"Michel Castelein&qu  2005-07-13 23:13:45 
Re: Assembler: alignment of machine instructions
richgr@[EMAIL PROTECTED]   2005-07-13 21:37:48 
Re: Assembler: alignment of machine instructions
Binyamin Dissen <posti  2005-07-14 11:26:02 
Re: Assembler: alignment of machine instructions
"arargh" arargh  2005-07-13 18:00:03 
Re: Assembler: alignment of machine instructions
glen herrmannsfeldt <g  2005-07-13 21:27:03 
Re: Assembler: alignment of machine instructions
glen herrmannsfeldt <g  2005-07-19 13:43:28 
Re: Assembler: alignment of machine instructions
Binyamin Dissen <posti  2005-07-14 11:26:04 
Re: Assembler: alignment of machine instructions
"John Small" &l  2005-07-14 10:50:59 
Re: Assembler: alignment of machine instructions
glen herrmannsfeldt <g  2005-07-25 16:03:55 
Re: Assembler: alignment of machine instructions
"Michel Castelein&qu  2005-07-26 08:25:21 
Re: Assembler: alignment of machine instructions
"Sven Pran" <  2005-07-27 09:45:31 
Re: Assembler: alignment of machine instructions
beu@[EMAIL PROTECTED] (B  2005-07-27 20:50:58 
Re: Assembler: alignment of machine instructions
"Sven Pran" <  2005-07-28 00:11:47 

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tan12V112 Thu Jul 24 0:44:34 CDT 2008.